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Perception FAQ

 

 

As a painter and professor of art - I constantly come across references that optical colour mixing, as in the art movement "pointillism" as well as ink jet printing involves both subtractive and additive mixing in the eye of the viewer. I completely disagree that two dots of colour, at sufficient distance, can 'additively' mix in the eye. I am not a colour scientist, my knowledge of this is entirely empirical, but I would be interested to hear your thoughts on the matter? Is it possible and if so, how?   (answer)

Is there any known research on trying to find colors outside of the color spectrum?   (answer)

The difference between "saturation", "chroma", and "colorfulness" can be very subtle. Can you explain? Similarly, is there any difference between the related terms "value", "lightness", and "brightness"? What do HSV and HSL describe?   (answer)

How come it is easier to see a certain color under low light condition while other colors are hard to see?   (answer)

Can females see more colors than males?   (answer)

Artists often find it difficult to identify subtle colors. Eg: is a warmer or cooler than another? Shadow and reflection are very hard. The more you stare the easier it is to convince yourself it is almost any color. I have heard that both saccadic eye movements and bending over so as to look at the subject upside-down can be helpful. Do you agree and do you know of any better techniques?   (answer)

I am studying the lightness differences in two types of dental crowns. Is there a minimum ΔL that is not perceived by humans?   (answer)

Does color have an objective existence?   (answer)

If the inability to differentiate blue and black and brown is caused by the gradual yellowing of the lens in our eyes, would wearing another color lens make it possible to see the colors?   (answer)

What is the most visible color for a motor cycle helmet?   (answer)

What education and degree is required to become a color scientist?   (answer)

Why does the S-cone see blue-red (i.e. violet) instead of pure blue? Where does the red come from without the L-cone?   (answer)

Why there is no spectral (pure) colors that can be reproduced by mixtures of other colors? It is just a coincidence of human color vision?   (answer)

I have a very old FM 100 Hue Test Kit (in a wooden box) but do not have a score sheet. I see all of the new kits have software. What came with this kit as it's obviously pre-PC.   (answer)

Why is it so difficulty to follow the process of saying the color of the word as opposed to saying the word itself?   (answer)

Which would yield the least visual discrepancies, a more chromatic color or less chromatic color?   (answer)

I bought a charcoal gray couch - love the color in the store. In my living room it looks dark blue! What color should I use on the walls and accessories to make it look gray again?   (answer)

What makes a color bright?   (answer)

I study the topographic influence on snow. When an individual looks at snow in shadow, they are actually seeing blue light, yet they state they see white. Is this based on learned experience of color? What effect does the question have, i.e. "What color do you see", vs. "What is the color of the snow?"   (answer)

Many auto accidents happen in early morning and late in the evening when it is dark outside. Does the vehicle color have anything to do with this? What automotive paint color is easiest for the eye to see when it is dark outside? How about in daylight?   (answer)

Although our sun is often depicted in artwork as "yellow", I have heard that it is actually "white", and that is why a white piece of paper appears white. Is this true? If so and we lived in a solar system with a different type of star, such as a red dwarf or a blue giant, would any objects appear "white", or would they take on the cast of their light source?   (answer)

When we compare luminosity of different hues, we find that blue is a relatively dark color, and yellow is a relatively light color. Do hues have an inherent luminosity independent of human perception?   (answer)

Are there studies of floral arrangement preferences of dichromats?   (answer)

The sensitivity of the human eye to color difference is greatest at approximately 550 nm. However, in interpreting the MacAdam ellipses , it would appear that humans are least sensitive to differences in color in this region. Why?   (answer)

How does aging affect color perception? Are older people able to discriminate brighter colors or softer colors better?   (answer)

Is it possible to explain color to a blind person if thay have never experienced it? Can the brain of a blind person assign a color to something if they know the shape but not the color?   (answer)

Why do different pure hues have differing lightness values?   (answer)

At what luminance (Candela per meter squared) in the ambient environmental light does scotopic vision turn to mesopic vision, or at what point can we start to see color? And at what point can we see the majority of colors?   (answer)

What is the most common first color that children recognize? The second?   (answer)

I am turning my formal dining room into an art gallery. We painted today and it is too bright. The way it looks now all you will see is the paint color and not the art. What are the best colors to paint a gallery, given that all the pictures are of different color schemes?   (answer)

In comparing light bulbs based on their color temperature, how much difference in color temperature is needed before an average person can notice that difference?   (answer)

How a mixture of R, G & B single wavelength sources (such as RGB laser) can produce white light even though they do not cover the whole spectrum?   (answer)

Why do we see colors when we spin a disc that contains figures in black & white?   (answer)

When job requirements demand color discrimination, how often should employees be tested on their color perception?   (answer)

Could you please tell me if there is any function that computes the chromatic adaptation and the color appearance for the various types of color deficiencies?   (answer)

I am a retinal surgeon. We sometimes stain the retina with trypan blue in order to highlight superficial membranes that need to be peeled (over the retina). Is there a colored contact lens that I could wear that would highlight the blue spectrum more so that it would be easy to see faint staining on trypan blue on the retina?   (answer)

At what distance, target size and viewing conditions (illumination level/type) does the HVS's ability to resolve color breakdown? Put another way, what is the "chromatic" resolving power of the HVS and how is that defined in terms of distance, size, viewing conditions?   (answer)

Is there a relationship between visual lightness (when we judge lightness of color) and Light Reflectance Value (a measurement that is expressed mathematically?   (answer)

I am a massage therapist. After a massage a customer said that when I had massaged her on a certain part of her body she could see a certain color, for ex. red, & at another spot she saw the color blue. Is there a reason to this?   (answer)

What is the color temperature that makes the road most clear during driving, even under unconditional weather?   (answer)

What is the unit of the viewing angle? Is it degree, radian or steradian?   (answer)

I am a Color Technician for a woman's retailer which specializes in black, white, and neutral only clothing. We test our associates with the Munsell 100 Hue test. Is there a similar test to evaluate for neutrals only?   (answer)

At what age do children develop good color perception?   (answer)

Can light be a "Brown" color? If not, why not?   (answer)

When purchasing an encapsulated Haz-mat suit, Level A, what colors have the best visibility for the different environments in which they might be used, i.e, sandstorms, snow, heavy rain, thick smoke, etc.?   (answer)

How does the eye determine the various colors of visible light?   (answer)

Why do black clothes appear blue in the artificial light of a clothing shop? Then when you take the item into natural light it is black? Why is that?   (answer)

The lighting goal for our new indoor shooting range is to have 100 footcandles of light on each target. Our question is this: should the walls and ceiling around the target be light in color or dark in color?   (answer)

I sometimes catnap at my computer or while reading and when I wake everything looks green tinged for about 20 seconds. Why?   (answer)

How does coloured text affect accommodation?   (answer)

Where can I buy Baker-Miller pink paint?   (answer)

Why are the colors of Christmas typically red and green?   (answer)

How long does it take for your brain to recognize color?   (answer)

Obviously having a single colour on two different stimuli (each encompassing a different meaning) on a workstation will cause confusion. What are these problems from a psychological, cognitive, or ergonomic perspective?   (answer)

Are the colors that we see during the day, present at night - only we cannot see them? Or are the colors that we see during the day not present, or altered, because of the low light?   (answer)

What are the evolutionary advantages and disadvantages of impaired color vision?   (answer)

Why does the greenery of parks and gardens look beautiful to our eye? Please elaborate with regard to perception and function of the eye.   (answer)

What the physical meaning of sharper cone reponse in CIECAM02?   (answer)

Why do boys choose blues, grays, black, and browns when coloring and girls choose more brighter colors like greens, reds, oranges when coloring?   (answer)

Do some people, through genetics, have dramatically different "rods and cones" in their eyes and see colors totally differently than "most people". This does not include colorblindness, but that some people might see red as yellow and blue as orange, etc. Is this true?   (answer)

Are there any estimates of the probability that a photon impinging upon a cone photoreceptor will be absorbed by the visual pigment within the receptor? How does this probability change as the radiance is increased so that more of the pigment is in the bleached state?   (answer)

Can a person with a color deficiency learn colors and shades and be able to distinguish differences even if they are not able to see the exact color that a normal vision person might see?   (answer)

Would it be possible to correct color blindness (for computer users) by measuring a user's color sensitivity at various wavelengths, then adjusting the output of the monitor to compensate for it?   (answer)

I am a massage therapist trying to do research on what color is best to have in a massage room and how it affects the client, such as improves relaxation, promotes healing. Any guidance?   (answer)

Does the color of one's eyes (light colored vs dark color) have any effect on vision?   (answer)

Can the color of the bedroom walls prevent proper sleep? My husband sleeps fine in a blue room, but has trouble in a red room (same bed!).   (answer)

Are car color choices determined by age, gender or ethnic group?   (answer)

What are the differences in perception of color by males and females?   (answer)

What trends are typical when Munsell testing a group of people? Are there effects due to age, gender, education, or ethnicity?   (answer)

What color do most people answer when asked to name a color quickly?   (answer)

Is there any standard by which Munsell colors are called "light" or "dark" or are those terms that are too subjective so that they don't get used?   (answer)

Can you comment on how does the following colors affect human psychology when considered in relation to fashion designing: red, yellow, blue, green, orange, violet, brown, pink, white, black, grey?   (answer)

Are there any filters that can be placed over the eyes to make a substance, which is invisible to the naked eye, visible through the filter? Can you give an example?   (answer)

Is there a range of Munsell or L*C*h coordinates that would describe browns?   (answer)

What color is best to paint a room with hardwood floors to enhance productiivity?   (answer)

I am looking for products to protect my eyes from UV-C light (254 nm). What substances are opaque or reflect to UV-C light? How harmful is UV-C light to human skin and eyes? Can you suggest any protective measures I should take?   (answer)

Is there a certain color that has been proven to be least tiring to the eye on web page backgrounds?   (answer)

Why can't humans see colors that fall in the UV or IR part of the electromagnetic spectrum?   (answer)

How often should color vision testing be assessed if the ability to see colors is important in one's occupation?   (answer)

Can chromatic discrimination change over time or can it improve through practice?   (answer)

Any correlation between age and chromatic discrimination ability?   (answer)

Do any illnesses/physical characteristics/disabilities impact one's chromatic discrimination ability?   (answer)

How can a color display with three monochromatic lasers produce a finely rendered colorspace, with what seem like the appropriate pastels and everything?   (answer)

What are the different textures of colour?   (answer)

How do the eye and the brain work together to create the chromatic adaptation 'illusion' effect with colours? Also, why does looking at certain stimulus for certain lengths of time effect the time span of the adaptation?   (answer)

Is there any research on changing the colors of a light to improve a surgeons abilility to see in different surgical enviroments? Can you improve their contrast sensitivity like skiers do with colored lenses.   (answer)

What is the problem if a person sees both gold and silver as silver? This person also has red-green defects.   (answer)

What is the top that is black and white and makes pale colors when spun?   (answer)

I would like to perform the Farnsworth-Munsell 100 hue test on my monitor. Will this work? Can I have the values of each colour caps to form the colours?   (answer)

I am writing a story about colour for children. Can you help explain (in simple terms) how a rainbow works and how the mixing of just a few colours in printing pictures in papers works?   (answer)

How long does it take to perceive color? Are some colors perceived more quickly than others?   (answer)

Do people with light colored eyes have better night vision than people with dark colored eyes?   (answer)

When the 3 hands on a spinning toy (which are 3 different sizes, long, medium and short) spin around really fast, they leave 3 "trails" of light in concentric circles. Why do we see 3 complete circles of light all the time?   (answer)

Do humans have a natural affinity for certain sorts of colors more than others as compared to other creatures?   (answer)

Do insects that have UV sensitivity in their visual system see the UV portion of the spectrum as "color"?   (answer)

Is color limited to the interaction of light with an object and our eyes?   (answer)

If no light is falling on an object, does it still technically have a "color"?   (answer)

Does the color green inspire thought?   (answer)

How I can mathematically convert from CIELAB (D65,10�) to XYZ (D65,2�) or RGB?   (answer)

How do the colors you wear affect your appearance? What colors make you look certain ways?   (answer)

Why do we recognize uniqueness only for four colors, blue, yellow, green, and red? Is there any color map of unique hues in a visual system?   (answer)

Why is a red Popsicle red?   (answer)

What is the difference between value and chroma? If I add black or white to a color I am changing its value. How do I change its chroma?   (answer)

How does color affect our vision?   (answer)

What factors affect the intensity of color?   (answer)

Do different people see the same color in different shades? Why?   (answer)

How does one resolve the concepts of the 'scientific' (linear) color frequency model and the 'artistic' (circular) color wheel model in regards to color perception?   (answer)

I am a member of an internet forum dedicated to the Rubik's cube. What is the set of 6 colors (including black/white) that human eye is best able to discriminate?   (answer)

I am a competitive rifle shooter. Are there any colored filters to place in my rifle sight that would help to reduce eye fatigue or even simply aid in aligning things?   (answer)

What distance can humans still distinguish between different colors?   (answer)

Is black paint recommend for a boy's bedroom?   (answer)

Why are common soccer balls black and white?   (answer)

Is it possible to make a color that is not visible to the human eye?   (answer)

Do age and gender matter when seeing color?   (answer)

What hue can the human eye dicern the most shades of?   (answer)

Can the brain take a 2D image (eg: a picture) and convert it to a 3D image?   (answer)

Can you tell me what color eye shadow would look the best for a given complexion?   (answer)

Do different colors affect your eye sight different over time?   (answer)

What is the real meaning of color blind?   (answer)

Did humans use chromatic adaptation long ago, for example in hunting?   (answer)

Does the color of your eyes affect your vision? Do people with blue eyes have better vision than those with green?   (answer)

Do you know of any table of rgb value pairs that make up visual complementaries (colors that are afterimage of each other)?   (answer)

How does color affect our mood?   (answer)

I need an example or a graph help to explain why humans cannot see colors that fall in the ultraviolet or infrared part of the electromagnetic spectrum.   (answer)

How does the eye see colors that are moving very rapidly? (eg: a spinning color wheel)   (answer)

Which colour has the most easily visually discriminable levels of saturation? The literature seems to suggest blue violet as this has the most steps when white light is added in 'just noticeable' amounts - would you agree with this?   (answer)

Does the first color you see when you wake up effect your mood?   (answer)

Do you think people can remember words better from colored paper or white paper?   (answer)

I would like to do a science experiment on "Will male and females chose the color that has been associated with their gender?" For example, pink for girls and blue for boys. Can you help be to create a 5th grade science experiment to test this idea?   (answer)

Please explain the Bradford Chrmatic adaptation transform as a physical phenomenon and provide the mathematical basis.   (answer)

Can human eyes see noise? Or, can our brain recognize what's signal and what's noise?   (answer)

What would be the ideal color for drafting rooms or any rooms used by art students?   (answer)

Is there something like color adaptation? I was wearing a blue light filter over one eye and felt that the differnce in color perception between the right and left eye disappeared after some time. When removing the filter, color perception in the previously uncovered eye felt like wearing a blue light filter for a short period of time.   (answer)

If someone walked down the street, what color clothing or facial features would that person have for me to easiest remember him/her?   (answer)

Does age and sex determine what color car a person buys?   (answer)

I am doing a science project on what colors are easiest to see in the dark. Can you help me figure out what experiment I should do?   (answer)

How can people distinguish edges of objects? Is this a function of rods or cones, or some organs else?   (answer)

On what things color depend so that only some colors disappear while others remain?   (answer)

Where can I buy Baker-Miller Pink?   (answer)

Will we ever be able to see colours we have never have seen? When I tell other people about my wonder to have different perceptions they think it is bogus. Will genetics and medicine make it possible in the future? When?   (answer)

Why is it more difficult to say the color of the word when it is printed in a different color?   (answer)

How do I measure contrast?   (answer)

What are "suprathresholds" and "thresholds," with reference to color difference?   (answer)

I want to see what make-up shades and colours suit which skin tone, for a school project. Please get back to me with a colour wheel and and some useful information.   (answer)

Why does the spinning Benham top look colored? Is there any simple explanation of that phenomenon?   (answer)

People of my area prefer reddish black on textiles. What kind of black do people in your area prefer on textiles?   (answer)

Where can one buy an anomaloscope? Does an instrument exist that has a bipartite field like an anomaloscope but allows any combination of one or two monochromatic lights in each half of the field?   (answer)

What is colour? How is it detected?   (answer)

Is it true that only some dreams are in color, while others are in shades of gray?   (answer)

Sign language interpreters have always been taught that they should wear colors that are in contrast to their skin tone to create maximum visibility and minimize eye fatique. Is there a more scientific way to teach these principles? What does research tell us about clothing color and eye fatique?   (answer)

Somedays my eyes look green and other days they look more blue. What color of clothing or eye shadow would I wear to make them appear more green? What colors should I NOT wear if I don't want them to look blue?   (answer)

I am testing whether colored (red and blue) backgrounds enhance or detract from a person's ability to assemble puzzles. Have these experiments like this have been done before? Any idea which age groups to test?   (answer)

Blue colors wouldn't have to have higher UV reflectance than other colors and I am sure exceptions can be found. However, in general blue objects are reflecting highly in the short-wavelength end of the spectrum and that reflectance continues into the UV. Another way to look at it is that the wavelengths they tend to absorb are mainly longer than the the blue and UV wavelengths while other colors are largely absorbing the shorter wavelengths.   (answer)

Has research been done to determine how closely the color receptors in various species match what one might expect given their evolutionary environment?   (answer)

When driving at night, what colors on cars are easier to see and what colors are harder to see?   (answer)

I want to scan the Ishihara plates and create the same colors on my monitor. Can you help?   (answer)

I have a severe color vision deficiency. Can you help me modify images so I can see the world the way others do?   (answer)

In performing a mechanical task with several different colored backrounds, which colors would bring the most contrasting results in the efficency of which the task is performed?   (answer)

What is the best test for screening color vision in employees using penetrant fluorescent dyes to inspect manufactured metal items for defects?   (answer)

What is the best color to paint walls in a machine shop to enchance productivity?   (answer)

If the fovea contains no S cones why don't humans have functional dichromancy in foveal vision?   (answer)

How does the color pink affect the minds of males and females?   (answer)

Is there any standard Colorimetric values of this GSC (Gray-Scale Comparison Method) method used for visual assessment was used by Luo and Rigg?   (answer)

What's the minimum Δfreq or Δwavelength an average person can differentiate so as to recognize two different colors?   (answer)

Why do we have color vision, and what is the evolutionary drive for color vision? It is striking how colorful the man made environment is compared to natural settings. What was the selective pressure that made individuals with color vision survivors-breeders in our natural habitat?   (answer)

When is white not white?   (answer)

How does the yellowing of the lens with age affect: colour vision, scotopic vision and the contrast of tests charts that are spectrally neutral?   (answer)

I measure animal colouration, in particular contrast, which is dependent on spot size, not just area coverage. I cannot measure the spots on a lizard belly, but I can get a numerical matrix from a digital photo. Can you help me calculate perceived contrast?   (answer)

Can visual color discrimination be taught? Does color discrimination become better through practice? What affect does the aging of a person's eyes have on color discrimination?   (answer)

Why do painted walls of saturated complementary colors cause eyestrain when placed close to one another?   (answer)

Do you have any training materials to illustrate color that I could use as an educational tool?   (answer)

How should a color lab be designed? What colors should the walls and furniture be, so as not to influence the perception of color?   (answer)

My two eyes see color differently. What causes this?   (answer)

What are color vision deficiencies? How common are they?   (answer)

What is color?   (answer)

How do we see in color?   (answer)

What do we know about research done on colors & their meanings?   (answer)

What does it mean to be color normal?   (answer)

What parts of the eye are important for color vision?   (answer)

How do we select names for colors?   (answer)

How are cones organized in our eyes?   (answer)

What spatial and temporal processing takes place in the eye? the brain?   (answer)

What is chromatic adaptation?   (answer)

How do we characterize a person’s color vision?   (answer)

How many colors can we see?   (answer)




As a painter and professor of art - I constantly come across references that optical colour mixing, as in the art movement "pointillism" as well as ink jet printing involves both subtractive and additive mixing in the eye of the viewer. I completely disagree that two dots of colour, at sufficient distance, can 'additively' mix in the eye. I am not a colour scientist, my knowledge of this is entirely empirical, but I would be interested to hear your thoughts on the matter? Is it possible and if so, how? (928)
Do you think that a TV screen or computer monitor are accomplishing additive color mixing? They are and they are doing so with small dots that additively mix by spatial blurring in the eye. The simplest proof is that Grassmann's laws of additive color mixing, derived for superimposed lights, also hold perfectly well for adjacent spots (spatial blurring) and those that flicker quickly in time (temporal blurring). I don' t know what more I can say, it's been proven empirically time and time again. (Back to top)


Is there any known research on trying to find colors outside of the color spectrum? (927)
There's no such thing. The spectral limits of possible colors are defined by the response of the human visual system. It's a bit of a circular definition, but since the limits are defined by our vision, we can't possibly stimulate our visual system with energy beyond those limits.

However their are other creatures who have color vision that responds to types of energy we cannot see (e.g., some types of birds, fish, insects). Perhaps the most referenced of those is the honey bee. Bees can respond to ultraviolet radiation that we can't possibly see. If you google "bee color vision" you will find lots of information. Here's a link to one overview at . (Back to top)


The difference between "saturation", "chroma", and "colorfulness" can be very subtle. Can you explain? Similarly, is there any difference between the related terms "value", "lightness", and "brightness"? What do HSV and HSL describe? (925)
Starting with brightness and lightness, brightness is your perception of how much light is coming from a stimulus. On a sunny day, everything is brighter than under dim illumination. Lightness is the brightness of an object relative to the brightness of a white object under the same illumination. Thus, lightness is relative brightness and stays more or less constant across changes in illumination level. Value is a term that comes from the Munsell system and is synonymous with lightness.

There is a similar relationship with the chromatic terms. Colorfulness is analogous to brightness and refers to how much "color" (or difference from neutral) is perceived. Objects get more colorful when there is more light falling on them, just like they get brighter. Like lightness, chroma is relative colorfulness. It is the colorfulness of an object relative to the brightness of a white object under the same lighting. And like lightness, chroma is more or less constant across changes in illumination level. Then it gets more confusing because there is a second relative colorfulness term, saturation. Saturation is the colorfulness of an object relative to its own brightness (rather than a white). This might seem redundant with chroma (and it is), but it is something different and one of the reasons it exists is because sometimes colors are see without a white object to relate them to.

All of this has nothing to do with HSV and HSL since they are huge approximations to color appearance and are not in any way calibrated to visual perception. You should think of their usage of color appearance terms as nothing but a rough analogy. (Back to top)


How come it is easier to see a certain color under low light condition while other colors are hard to see? (924)
There are two possible reasons.

One is that the color of the light might be changing. For example in low light outside the light tends to be more blue since the sun has set. This makes blue objects lighter and easier to see and red objects darker and more difficult to see. Secondly, the sensitivity of the visual system shifts toward blue for lower light levels. This causes the same effect described above.

In most cases, it is a combination of the two effects. (Back to top)


Can females see more colors than males? (920)
No. Color discrimination varies from person to person, but females have no specific advantage. That assumes normal color vision. Males, however, are far more likely to have a color vision deficiency (color blindness) with about 8% of the male population having a deficiency and less than 0.5% of the female population having a deficiency. If you are comparing males and females with normal color vision, then there's no difference. If you choose random females and males, you are far more likely to run into a male with a deficiency. (Back to top)


Artists often find it difficult to identify subtle colors. Eg: is a warmer or cooler than another? Shadow and reflection are very hard. The more you stare the easier it is to convince yourself it is almost any color. I have heard that both saccadic eye movements and bending over so as to look at the subject upside-down can be helpful. Do you agree and do you know of any better techniques? (919)
This is a great question and as you might have guessed, more complicated than it seems.

Our perception of color depends tremendously on context (think about demonstrations of simultaneous contrast or afterimages) and part of what our visual system does is to remove subtle changes in color through mechanisms of chromatic adaptation in order to more easily detect the more significant changes (such as important objects in a scene). This adaptation is one thing that makes it difficult to discern subtle gradations in color, shadows, etc. Some quick eye movements back and forth between areas in a scene will indeed help since it will tend to set your state of adaptation to some intermediate level rather than adapting to, and therefore becoming less sensitive to the color of, a certain area. We also tend to associate colors with known objects (e.g., the same physical yellow might look different on a banana than it would on a car) and if we can isolate the color stimulus from the object we can sometimes better identify the physical color present. Your suggestion of looking at objects upside-down is a step in this direction; it would tend to isolate the color perception from the object perception and make it a bit easier to identify the color. Another way to do this is with a reduction screen or aperture. Cut a small hole in a piece of neutral cardboard and look through it at the object. This will allow you to focus on the edge of the hole and see the color behind in isolation from the object. I'm sure there are other tricks that artists have come up with, but these do indeed help. (Back to top)


I am studying the lightness differences in two types of dental crowns. Is there a minimum ΔL that is not perceived by humans? (916)
The minimum perceptible change in L* depends on the samples and viewing conditions. Often a value of 1.0 is used as a general rule. However, for large uniform samples on a uniform background at a high illumination level, people can see smaller differences. In your case, you have a fairly complex stimulus (the crown) in a very complex and poorly illuminated environment (the mouth), so I would think it is very safe to say that nobody could see a difference less than 1.0. You might even be safe with differences of 2-3 units. (Back to top)


Does color have an objective existence? (915)
Yes. But perhaps not in the way you are thinking. Color is defined as a human perception and therefore does not exist outside of humans. Objects and light sources do not have a color unless someone is there to observe them. (They do have spectral power properties that provide the stimulus for color, but the actual perceived color depends on those as well as attributes of the human observer.) That said, perceptions can be just as objective as physical objects. In the laboratory, we are able to complete repeatable, objective experiments to measure observers' color perceptions. That makes the perception of color, and therefore color itself, an objective phenomenon ... even though it is "only" a perception. (Back to top)


If the inability to differentiate blue and black and brown is caused by the gradual yellowing of the lens in our eyes, would wearing another color lens make it possible to see the colors? (914)
The yellowing of our lens with age does contribute to our inability to distinguish black, blue, and brown in dim lighting, but the dim lighting is probably a bigger factor. The yellowing of our lens means that less blue light gets through to our retinas, but dim incandescent bulbs also contain very little blue light. The lack of blue light to respond to is what causes these particular difficulties with dark colors.

Unfortunately it can´t be fixed with a filter. Another filter would just take away more light and, even if that light was of a different color than blue, less light makes it even harder to distinguish colors. The best answer is to look at the colors (typically socks!) under brighter light and, if possible, bluer light such as natural daylight. (Back to top)


What is the most visible color for a motor cycle helmet? (912)
I ride a motorcycle and I did a lot of research into this question before I purchased my helmet. White helmets are significantly more visible than darker helmets and the visibility of the rider is a significant factor in motorcycle helmets. Those conclusions also make sense from a color science perspective. My helmet is white and I wouldn't choose any other color. Also, the addition of a bit of reflective tape makes the helmet/rider much more visible at night and twilight. (Back to top)


What education and degree is required to become a color scientist? (911)
At RIT, someone can get M.S. and Ph.D. degrees in Color Science and either of those are excellent qualifications to become a color scientist. Such degree programs are rare; in fact RIT's is the only program in Color Science in the United States. However, there are plenty of color scientists out there who have degrees in other fields and then learned more about color science through their work or research. The students in our graduate programs also come from these various fields with undergraduate degrees in areas such as physics, chemistry, biology, mathematics, psychology (perceptual or experimental), cognitive science, computer science, etc. (Back to top)


Why does the S-cone see blue-red (i.e. violet) instead of pure blue? Where does the red come from without the L-cone? (910)
To understand the appearance of short wavelengths of light as violet, you have to look beyond just the cones in the visual system. As you suggested, the S-cones only respond to short-wavelength light and the L-cones to long-wavelength light. At the next conceptual step in visual processing is when the cone signals are combined into opponent-colors signals. These are three signals that respond to light vs. dark, red vs. green, and yellow vs. blue. The light-dark signal is derived from summing all three cone types. The yellow-blue signal is obtained by adding the L and M cones together to get a yellow response and subtracting the S cone signal to get an opposing blue response. The red-green signal is obtained by adding the L and S cones together to get the "red" response and subtracting the M cones to get an opposing green response. Thus, our perception of "redness" depends on signals that originate in both the L and S cones. Of course, this is greatly simplifying what happens in the visual system, but it is the general concept behind the appearance of "violet". (Back to top)


Why there is no spectral (pure) colors that can be reproduced by mixtures of other colors? It is just a coincidence of human color vision? (909)
Actually, you can match some spectrally pure colors with mixtures of other colors. For example, you can match a yellow-appearing wavelength with mixtures of red- and green-appearing wavelengths.

However, the cases in which this is possible are somewhat limited. In general, the limitations of what colors can be produced by mixing other colors depends on the colors being mixed, the method of mixing (e.g. additive vs. subtractive) and also the properties of the human visual system. (Back to top)


I have a very old FM 100 Hue Test Kit (in a wooden box) but do not have a score sheet. I see all of the new kits have software. What came with this kit as it's obviously pre-PC. (908)
The old tests came with an instruction manual and pad of score sheets. I am not sure if it is still possible to purchase the score sheets, but I did find a PDF containing both through a Google search. See www.qcqa.com. (Back to top)


Why is it so difficulty to follow the process of saying the color of the word as opposed to saying the word itself? (906)
This is called the "Stroop Effect". If you do an internet search on that term, you will find many demonstrations and explanations. The basic concept is that our brains more easily identify words than colors so it is easier to say the word than the color. (Back to top)


Which would yield the least visual discrepancies, a more chromatic color or less chromatic color? (904)
This is a difficult question to answer because it all depends on how the color is measured and color scientists work to create color metrics where the answer is that they are equal. However, one point to consider is that there is more potential for significant variations in perception for less chromatic colors, especially grays. For example two people viewing the same near-gray sample might use completely different hue names (e.g., one saying it is bluish and the other reddish) while such name changes would be unlikely to occur for a highly chromatic color (both people more likely to give it the same name). (Back to top)


I bought a charcoal gray couch - love the color in the store. In my living room it looks dark blue! What color should I use on the walls and accessories to make it look gray again? (902)
To make something appear less blue (more neutral) you would need to surround it with objects that are even bluer. It is likely that the environment in your home (including the illumination) is more yellow than what you saw in the store and this makes your couch appear a bit more bluish through simultaneous contrast. (Back to top)


What makes a color bright? (898)
A color looks bright when it both reflects a lot of light and is very colorful. A white object under a lot of illumination will look bright, but a very colorful yellow object under a similar amount of illumination might look even brighter because it is colorful in addition to reflecting a lot of light. (Back to top)


I study the topographic influence on snow. When an individual looks at snow in shadow, they are actually seeing blue light, yet they state they see white. Is this based on learned experience of color? What effect does the question have, i.e. "What color do you see", vs. "What is the color of the snow?" (897)
Great question! First keep in mind that color is a perception and not a physical property of light. There is a relationship of course, but it is not as direct as one might think. If they say the snow is white, then it is. The fact that a stimulus with more energy in the blue region of the spectrum (snow in the shadow) can still look white is due to chromatic adaptation. Our visual system adapts to changes in the color of the illumination and the result is that object colors like the white snow tend to appear relatively constant across the changes in illumination. Some observers can learn to separate the effects. Artists often do this and can distinguish easily between the color of the object (or material) and the color of the light reaching the eye. (Back to top)


Many auto accidents happen in early morning and late in the evening when it is dark outside. Does the vehicle color have anything to do with this? What automotive paint color is easiest for the eye to see when it is dark outside? How about in daylight? (895)
I have not seen any statistics correlating car color with accident rates. Accidents are not common enough and there are two many other variables involved to get the required statistics. However, there is little doubt that visibility is one important factor in automobile accidents (this has been shown for motorcycle accidents since they are often "not seen" by other drivers). The most visible car color (and motorcycle helmet color for that matter) is white in low light conditions. This is because it reflects the most light and normally contrasts the most with the background (a snowy background would be an exception where a black car might actually be more visible). In general white is also most visible in the daylight because it contrasts most with the typical background. (Back to top)


Although our sun is often depicted in artwork as "yellow", I have heard that it is actually "white", and that is why a white piece of paper appears white. Is this true? If so and we lived in a solar system with a different type of star, such as a red dwarf or a blue giant, would any objects appear "white", or would they take on the cast of their light source? (894)
Our sun is yellow in comparison with our blue sky. What looks white to us can be produced by a wide range of visual stimuli since our visual system is able to adapt to the color of the illumination. That adaptation is why a white piece of paper looks white under a variety of light sources (outside on a sunny day it is illuminated by the yellowish sun and the bluish sky together). If we lived under a sun of a different color, we would still adapt and objects would appear roughly the same as they do now (at least that white piece of paper would still look white). (Back to top)


When we compare luminosity of different hues, we find that blue is a relatively dark color, and yellow is a relatively light color. Do hues have an inherent luminosity independent of human perception? (887)
No. It is due to the spectral response of the human visual system. Anything you see in a rendered black and white image is caused by the spectral response of the imaging system ... which is often designed to mimic the human visual system. (Back to top)


Are there studies of floral arrangement preferences of dichromats? (882)
Unfortunately I am not aware of any such studies. However, you might want to look at the website vischeck.com. It allows you to upload images and then see what they might look like to people with color vision deficiencies. While the rendered colors might not be accurate, it would at least let you see which colors become indistinguishable. By testing some images of floral arrangements you would be able to see if the various flowers contrast more or less, etc. (Back to top)


The sensitivity of the human eye to color difference is greatest at approximately 550 nm. However, in interpreting the MacAdam ellipses , it would appear that humans are least sensitive to differences in color in this region. Why? (880)
Humans are most sensitive to light at 555nm (when using their cones), but that is a response to seeing, or not seeing, a light stimulus at all, not to distinguishing a color difference. It really is pretty much impossible to say what color people are most sensitive to since any measure would depend on the color space used. MacAdam ellipses in xy are definitely not the way to go. First they represent the results of only a single observer and second they are just showing the non-uniformity of the xy diagram, which really has no direct physiological significance with respect to color discrimination. (Back to top)


How does aging affect color perception? Are older people able to discriminate brighter colors or softer colors better? (877)
As we age, the lens in our eye begins to absorb and scatter more blue light (it becomes yellower). This causes a decrease in visual sensitivity to shorter wavelengths that make us less sensitive to blue colors and less able to discriminate purple and red colors. There also tends to be more of a negative effect of glare as we age. So really, no colors are discriminated better as people get older and whether brighter or softer colors are preferable would probably depend on the particular person and the illumination and viewing conditions. (Back to top)


Is it possible to explain color to a blind person if thay have never experienced it? Can the brain of a blind person assign a color to something if they know the shape but not the color? (875)
We can not say for sure, but I would think this would be impossible. It is very difficult to describe colors of objects to a seeing person and all of the definitions of color use examples. If one has never experienced the examples, then it seems it would be extremely difficult, if not impossible, to give them an impression of color appearance. (Back to top)


Why do different pure hues have differing lightness values? (873)
The perception of lightness is complicated and depends on many variables. However a simple way to look at this question, that does explain most of what is observed is to think about our relative sensitivity to light of various wavelengths through the visible spectrum. In general we are more sensitive to wavelengths in the middle of the spectrum (approximately green) than to those at the ends (approximately blue and red). A pure green hue will be made up of light that we are very sensitive to and thus generally have a higher lightness than a pure red, blue, or purple (which is made up of red and blue). Of course it is possible to create stimuli that do not follow this trend, but for reflecting objects, or lights with equal amounts of energy, this general rule will hold. Usually highly saturated greens and yellows have a relatively high lightness, while reds, blues, and especially purples have a relatively low lightness. (Back to top)


At what luminance (Candela per meter squared) in the ambient environmental light does scotopic vision turn to mesopic vision, or at what point can we start to see color? And at what point can we see the majority of colors? (868)
The specific answer would depend on the individual observer, viewing conditions, and the state of adaptation. However at approximately 1 cd/m^2 the responses of rods and cones are equal, so this is essentially the midpoint of the mesopic region; some color is visible. As a rule of thumb, you could assume that reasonably good color vision (majority of colors) is present at 10 times that luminance (10 cd/m^2) and that no color vision is present at 10% of that luminance (0.1 cd/m^2). (Back to top)


What is the most common first color that children recognize? The second? (867)
I don't think I can answer any better than this website. Vision works on contrast, not individual colors. The first is light-dark contrast, so you could say that infants can see white, black, and grays first. This is probably followed by red-green discrimination and then yellow-blue discrimination. (Back to top)


I am turning my formal dining room into an art gallery. We painted today and it is too bright. The way it looks now all you will see is the paint color and not the art. What are the best colors to paint a gallery, given that all the pictures are of different color schemes? (863)
The best colors for walls tend to be of medium lightness (perceptually half way between white and black). That way both the light and dark areas of the artwork can contrast with the background. Theoretically, the ideal color is also a neutral gray, but that can become monotonous, especially in a home. The selected color is not nearly as important as the lightness, but it is best to avoid any very saturated colors. Pick a color of medium lightness, that is a hue you like, but not very saturated. (Back to top)


In comparing light bulbs based on their color temperature, how much difference in color temperature is needed before an average person can notice that difference? (861)
It would depend on the viewing conditions. For example, if the two bulbs were viewed side-by-side, then a smaller difference would be perceptible than if the bulbs were viewed one at a time. However in general, it is probably reasonable to assume that a difference of about 100K or greater is perceptible. (The actual value will also depend on the initial color temperature as well with the change required to see a difference becoming larger at higher color temperatures.) (Back to top)


How a mixture of R, G & B single wavelength sources (such as RGB laser) can produce white light even though they do not cover the whole spectrum? (851)
Three appropriate lasers are sufficient to stimulate the three types of cone receptors in our visual system to the same degree that they would be by a continuous spectrum. Thus, we are not able to perceive the difference. This property is known as metamerism. (Back to top)


Why do we see colors when we spin a disc that contains figures in black & white? (848)
These colors are referred to as Benham's colors or Fechner-Benham colors. Here is a nice explanation of the Benham top. Also, if you do a web search on those terms you can find a lot of information and theories. (Back to top)


When job requirements demand color discrimination, how often should employees be tested on their color perception? (847)
A person's overall color vision (normal vs. defficient) rarely changes in their lifetime. However color discrimination ability might. So everyone should be checked at least once and it is probably reasonable to repeat the tests every few years, but not really necessary to do it more often than that. (Back to top)


Could you please tell me if there is any function that computes the chromatic adaptation and the color appearance for the various types of color deficiencies? (840)
I am not aware of any models specifically designed to compute chromatic adaptation and color appearance for color deficiencies. The closest I can think of is the model implemented and described at vischeck.com. While it does not produce predictors of appearance, one might take the simulated output of their model as calibrated RGB input into a color appearance model such as CIECAM02 in order to obtain approximate appearance. (Back to top)


I am a retinal surgeon. We sometimes stain the retina with trypan blue in order to highlight superficial membranes that need to be peeled (over the retina). Is there a colored contact lens that I could wear that would highlight the blue spectrum more so that it would be easy to see faint staining on trypan blue on the retina? (834)
If you are trying to see a light blue on a pale background, then the best thing to do would be to use light that is absorbed strongly by the blue, but not by the background. That would be yellow or red light (which would also be reflected strongly by any red tissue). You can accomplish the same effect with either lighting or lenses, although it might be a little easier to discriminate by briefly changing the color of the lighting since you won't adapt to the color change as much as you would wearing colored lenses. (Back to top)


At what distance, target size and viewing conditions (illumination level/type) does the HVS's ability to resolve color breakdown? Put another way, what is the "chromatic" resolving power of the HVS and how is that defined in terms of distance, size, viewing conditions? (821)
In your observed scene, there are two things happening. The stimuli are getting smaller, but they are also becoming physically more similar due to the intervening atmosphere. If they were far enough away, all you would see is atmosphere (or imagine the atmosphere was more optically dense, like on a foggy day) and you couldn't discriminate them at all. So, first of all, that physical change needs to be accounted for. After that, there are changes in your visual system as well. Viewing conditions make all the difference in the world and cannot be explained in a short answer (I wrote a whole book on that entitled "Color Appearance Models"). However, as the stimulus becomes small in viewing angle, you do lose your ability to distinguish color. Once the stimulus is smaller than about 0.25 deg, you are close to becoming a dichromat (it's called small area tritanopia) due to the small numbers of blue-sensitive cones. Then when it gets even smaller, maybe 1-2 minutes of arc, you really can't discriminate color at all (only brightness). This is why stars look far more colorful in images than they do to the naked eye (even those that are bright enough to see with cones). (Back to top)


Is there a relationship between visual lightness (when we judge lightness of color) and Light Reflectance Value (a measurement that is expressed mathematically? (818)
Yes, they can be related mathematically. One way is through the CIELAB L* equation. L* is intended to represent perceived lightness (your grayscale judgement) with a perfect white at 100, a perfect black at 0, and a perceptually middle gray at 50. It is a function of the Y tristimulus value, or luminance (which is also your LRV). That perceived middle gray with an L* = 50 has Y = 20. The particular equation is a cube root function with an offset. L* = 116(Y/Yn)^(1/3) - 16.

Yn is the Y value for a perfect white under the given viewing conditions. I hope this helps. (Back to top)


I am a massage therapist. After a massage a customer said that when I had massaged her on a certain part of her body she could see a certain color, for ex. red, & at another spot she saw the color blue. Is there a reason to this? (817)
There are two possible reasons that I can think of. One is something called a pressure phosphene. They usually happen when you gently touch the side of your eye and you can see some colors. It is possible that the massage in different areas cause differing pressure on the eyes (depending on the position your client was in). A second possibility is a phenomenon called synesthesia. This is when stimulation of one sense produces a response in another sense. For example massage in certain areas might produce the red impression along with a feeling of slight pain (as a random example) while the massage in another area might have produced a blue sensation along with a soothing feeling (another random example). (Back to top)


What is the color temperature that makes the road most clear during driving, even under unconditional weather? (811)
I am not familiar with any research on this topic, but some might exist. My understanding is that moderate color temperatures (say around 4000K) are being used as a trade-off between the traditional halogen lamps that are too yellow to render colors well and the bluer discharge lamps that tend to produce a lot of visual glare for oncoming traffic. That might well be the best compromise. (Back to top)


What is the unit of the viewing angle? Is it degree, radian or steradian? (805)
"Degree" is the unit typically used. However degrees and radians are interchangeable (like yards and meters they measure the same thing). Steradians, on the other hand, are used to measure solid angles like cones and are not appropriate for viewing angles. (Back to top)


I am a Color Technician for a woman's retailer which specializes in black, white, and neutral only clothing. We test our associates with the Munsell 100 Hue test. Is there a similar test to evaluate for neutrals only? (802)
There appear to have been some developed. If you do a search on "lightness discrimination test" you can find some references. However, I am not aware of a commercially available test similar to the Farnsworth-Munsell test. It wouldn't be difficult to create one of your own. You would just need to make a set of gray samples closely spaced in lightness (perhaps 100 or so from white to black) and then ask people to put them in order. You could score it in the same way as the normal Farnsworth-Munsell test. (Back to top)


At what age do children develop good color perception? (790)
The visual system of infants is still developing after birth. It is difficult to say exactly how long it takes color vision to become "normal", but by about 6 months of age the visual system is essentially the same as an adult. More significant, probably, is that visual acuity improves rapidly during those first six months and stimulation of all types from the visual world does aid in this early development. Here is a link to a good page on infant vision. (Back to top)


Can light be a "Brown" color? If not, why not? (787)
This is one of my favorite questions. The short answer is "no". Brown cannot be perceived as a light source because it is only perceived as a related color that is "dark" and "low in chroma". This can only occur for colors that are less luminous than the white we are adapting to. Here is some more detail from one of my other websites.

Q: What is brown?
A: Brown is dark, low-chroma (desaturated), orange. In other words, an orange light that is perceived in an environment that makes it look dark and less saturated will appear brown. A brighter surround is such an environment. Brown is a special sort of color perception that requires this relationship to its environment in order to be perceived. That's why you can't go to a hardware store and buy a brown light bulb!" (Back to top)


When purchasing an encapsulated Haz-mat suit, Level A, what colors have the best visibility for the different environments in which they might be used, i.e, sandstorms, snow, heavy rain, thick smoke, etc.? (785)
The best color for each situation will be different. The thing to keep in mind is that the visual system functions on contrast, the differences between colors of objects. For example in a snowstorm with snow on the ground, black would be by far the best color (most contrast with white), even at night. In thick smoke or heavy rain at night, black would probably be the absolute worst color. White would be the best then with respect to contrast. However a secondary consideration is that you want them to stand out from other common objects. In that case, you would want a very light color that is rare (like blaze orange or fluorescent yellow-green). (Back to top)


How does the eye determine the various colors of visible light? (777)
Our perception of colors comes from a combination of the sensing of light in the eye and the processing of that information in the brain. The first step is that we have three types of cone receptors in the eye that respond to different wavelengths of light. Approximately, they respond to red, green, and blue light respectively. It is the responses of these three receptor types, in various proportions, to the light present in a scene that initiates the process of color vision. (Back to top)


Why do black clothes appear blue in the artificial light of a clothing shop? Then when you take the item into natural light it is black? Why is that? (775)
There are many types of artificial light and the interactions of light with objects can have very significant effects on the perception of the object color. It all depends what the material is made of and how it is colored. However, you might be seeing a purely perceptual effect. If the lighting is yellowish (like incandescent lamps), then there is a visual contrast effect (technically called the Helson-Judd effect) that makes darker colored objects appear bluish. What is happening is that the in contrast to the overall yellowness of the scene, our visual system adapts and where there is little light (the dark objects) our we notice the perceptual opposite of yellow, which is blue. It is always best to judge colors of objects under the variety of lighting in which they will be used (or worn). (Back to top)


The lighting goal for our new indoor shooting range is to have 100 footcandles of light on each target. Our question is this: should the walls and ceiling around the target be light in color or dark in color? (770)
I would make them light in color since this will increase the perceived contrast of the targets themselves and make them essentially more visible. Although with the intense focus on the target that usually accompanies shooting, the effect might be very small. (Back to top)


I sometimes catnap at my computer or while reading and when I wake everything looks green tinged for about 20 seconds. Why? (757)
This can be explained by chromatic adaptation. If you close your eye and look toward a light source you will notice that you can perceive some red light passing through your eyelids. When your eyes are exposed to this red light for a while (while you nap), they become relatively less sensitive to red light and therefore relatively more sensitive to green light. When you open your eyes, they are exposed to the world of fairly neutral light, but since your eyes are more sensitive to green light, everything appears to have a tinge of green for 20 seconds or so. This is the same effect as chromatic afterimages that cause you to see one color after staring at another for a while. (Back to top)


How does coloured text affect accommodation? (750)
There are two ways that the color of text impacts accommodation. The first is simply through luminance contrast. Text that has more luminance (or lightness) contrast is easier for us to focus on. For example black on white has far more contrast than yellow on white (or blue on black). Secondly, there is chromatic aberration in the eye, so if we are focused on text of one color, it is quite possible that text of another color will be out of focus and require us to accommodate again to read it. (Back to top)


Where can I buy Baker-Miller pink paint? (739)
I don't know of any particular source for Baker-Miller pink paint or even a standard definition of what it is. Your best bet would be to find a sample of the color you want and then go to a paint store to have them custom match it for you. However, you might want to do some more research on the topic as well. The reason there is no standard color is probably because the effects of calming people are not consistent from person to person and the pink exposure has also been shown to enrage people if they are left in pink rooms too long. I think the effect is more folklore than well-understood science. There are certainly emotional effects of color, but they are not consistent from person to person. Faber Birren's book "Color and Human Response" is a good introduction to the topic. There is also this Color Matters page with a little more information on Baker-Miller pink. (Back to top)


Why are the colors of Christmas typically red and green? (731)
There are various stories and theories, but this explanation seems to capture the essence of several of them. (Back to top)


How long does it take for your brain to recognize color? (729)
This is not an easy question to answer since it will depend on many variables including the way the color is presented and the response required from the observer. For example, you might be able to recognize a color (or color change) in a very short pulse of light, but it could take you significantly longer to produce the word required to describe the color. Unfortunately there is no simple answer for this question. However, if you type the words "color", "reaction," and "time" into google, you will find lots of resources that describe and demonstrate various experiments that might be helpful. (Back to top)


Obviously having a single colour on two different stimuli (each encompassing a different meaning) on a workstation will cause confusion. What are these problems from a psychological, cognitive, or ergonomic perspective? (725)
I received the following suggestions from a colleague far more knowledgeable than me in this area....

Here's a relevant article: Smallman, H. S. & Boynton, R. M., Segregation of basic colors in an information display, J. Opt. Soc. Am. A, Vol. 7, No. 10, 1990.

This site is also very helpful: colorusage.arc.nasa.gov

Also of interest: colorbrewer.org

There is also a book by Colin Ware called Information Visualization: Perception for Design that is supposed to be quite good. (Back to top)


Are the colors that we see during the day, present at night - only we cannot see them? Or are the colors that we see during the day not present, or altered, because of the low light? (724)
The physical stimulus for color is still there, it's just that the amount of light is reduced to the point that we can no longer perceive color. For example, if a photograph is taken with long enough exposure time the colors will look just like a daytime photograph. So in terms of your question the "colors" are still there, we just cannot see them. (Back to top)


What are the evolutionary advantages and disadvantages of impaired color vision? (722)
It is thought that normal trichromatic color vision provides advantages for finding healthy food and healthy mates, both of which are selective advantages for evolution. However, it is clear that people with color vision deficiencies can function quite well in the world and therefore there hasn't been enough of a disadvantage of these deficiencies to make them fade away through evolution. There are even reports of some situations in which color deficient observers can see patterns that are masked by all the color variation that normal observers might see. (Back to top)


Why does the greenery of parks and gardens look beautiful to our eye? Please elaborate with regard to perception and function of the eye. (698)
Those same green colors might look quite ugly in a different context. It is the context of the objects, their setting, their meaning to us, and our associations of colors with all of those features that helps us perceive beauty. Ultimately, all of those stimuli are being associated with with pleasant experiences. It could also be considered that the perceived beauty of the plants is an evolutionary advantage for them because it encourages humans to take care of them. (Back to top)


What the physical meaning of sharper cone reponse in CIECAM02? (693)
There is no direct physical meaning to these sharpened responses in terms of cone responses. They are not cone responses at all (as is clear from the negative parts of the curves). Instead, they represent combinations of cone responses that could potentially exist at higher levels of the visual system. The result is that these responses, together with multiplicative normalization, seem to fairly well model the overall processes of the visual system. Sharpened responses produce a chromatic adaptation transform with predictions closer to perfect "color constancy" and it makes sense that von Kries scaling in the actual cone responses combined with other mechanisms of adaptation at higher levels would also result in such responses. (Back to top)


Why do boys choose blues, grays, black, and browns when coloring and girls choose more brighter colors like greens, reds, oranges when coloring? (689)
I don't know of any research on the topic. There is some information on color popularity on the Crayola website, so there might be some information there. I would suspect the preferences are not well separated by gender at a young age. (Back to top)


Do some people, through genetics, have dramatically different "rods and cones" in their eyes and see colors totally differently than "most people". This does not include colorblindness, but that some people might see red as yellow and blue as orange, etc. Is this true? (688)
I am not aware of any research that would suggest such unique visual systems, so to answer your question I'd have to say "no" it's not true. Beyond typical color vision deficiencies, there are small genetic differences in the color sensitvities of the three cone types, but these are very small differences and nothing that would produce qualitiatively different visual percepts (like seeing blue as orange, etc.). Of course, we can never be sure that everyone's internal perceptions are identical, but there is plenty of evidence to suggest that our overall responses to color stimuli are very similar. (Back to top)


Are there any estimates of the probability that a photon impinging upon a cone photoreceptor will be absorbed by the visual pigment within the receptor? How does this probability change as the radiance is increased so that more of the pigment is in the bleached state? (685)
This question is not as easy to answer as it might seem. I am not aware of any specific estimates. For the optimal conditions with a cone dark adapted, optimal wavelength, etc. the probability that a photon incident directly on the cone will be absorbed is probably quite close to 1. That probability would gradually reduce to zero as the photopigment is bleached, but it takes an extreme amount of exposure to bleach a significant amount of photopigment. The real limits on visual perception are actually getting the photons to be incident on the cone in an optimal way. The probability would depend on the direction and location of the photon in addition to its wavelength. The classic work of Hecht, Shlaer and Pirenne, "Energy, Quanta, and Vision", The Journal of General Physiology 25, 819-840 (1942) describes how photons are lost in the visual process and how single photons incident on each a collection of rods are adequate to produce a visual response. It is generally accepted that cones are only slightly less sensitive to light, but respond individually, rather than in groups and therefore need more photons in a single receptor. You might also look at this website for a brief overview and chapter 7 in the classic text "Vision and Visual Perception" edited by Graham also provides some more details. (Back to top)


Can a person with a color deficiency learn colors and shades and be able to distinguish differences even if they are not able to see the exact color that a normal vision person might see? (684)
Yes. Many color deficiencies still allow the observers to see quite a range of colors and learn to associate appropriate names with those colors. There will still be some cases where there is confusion (depending on the particular deficiency), but it is really quite amazing how well people can get by. You can learn some more and see some images at vischeck.com. (Back to top)


Would it be possible to correct color blindness (for computer users) by measuring a user's color sensitivity at various wavelengths, then adjusting the output of the monitor to compensate for it? (683)
Unfortunately not. For some observers, a simple boost in one of the primaries might help, but it is more likely that their own mechanisms of chromatic adaptation have already taken care of that. For dichromats, they are missing one of the cone responses and there is nothing you can do with the stimulus to correct for that. The best you can do is make sure that the stimulus doesn't contain colors they would confuse with one another. You can find lots more information on this topic at vischeck.com. (Back to top)


I am a massage therapist trying to do research on what color is best to have in a massage room and how it affects the client, such as improves relaxation, promotes healing. Any guidance? (681)
There is no single answer. It would really depend on the particular client. You are probably best off with a muted color (near neutral) that is not likely to seem offensive to anyone. Blue is the most popular color as a "favorite color", so maybe a grayish-blue would be good. You then will probably have the best results by allowing the client to decide the lighting level (again keep the color fairly neutral to avoid being offensice). Personally, I would close my eyes and the color of the walls wouldn't matter at all. (Back to top)


Does the color of one's eyes (light colored vs dark color) have any effect on vision? (675)
There is no evidence that eye color has an effect on visual performance. (Back to top)


Can the color of the bedroom walls prevent proper sleep? My husband sleeps fine in a blue room, but has trouble in a red room (same bed!). (674)
Can the color of the bedroom walls prevent proper sleep? My husband sleeps fine in a blue room, but has trouble in a red room (same bed!).It is possible, but not likely just becuase of the color stimulus. For example, if he entered a room that was already dark he would have no way to know the color and it could not possibly affect his sleep. However, that is not the case here. I am sure he knows the color before he tries to sleep and it might have some impact. Perhaps he is just less comfortable in a pink room. Since you have asked the question, this might indicate that it is an issue for him (for whatever reason). Also, you shouldn't necessarily jump to the conclusion that it is the color since I am sure there are other things that are different about the two rooms ... it might be something else. Some even think the direction the bed is pointing matters. (Back to top)


Are car color choices determined by age, gender or ethnic group? (673)
Almost certainly "no". There would definitely be societal preferences and since people often tend to group themselves according to the dimensions you listed and "like what their friends like", you could probably find some correlation. However, it is quite rare that someone purchases a car that is their preferred color. First of all, not that many people special order a car. Instead they purchase what is on the lot and available for a perceived better price. Secondly, most cars only come in a limited range of colors. These two facts of the automobile market mean that measures of the colors sold and peoples' preferences bear little relationship to one another. It is an interesting topic and there are those who spend a lot of time "predicting" what colors people will like in forthcoming products. However these predictions are self-fulfilling prohpecies since the manufacturers use the predicitons to put the products out into the market and people are forced to purchase what is available. They will capture longer-term trends, but not short-term predictions. One organization involved in this sort of market research is the Color Association of the U.S. See (Back to top)


What are the differences in perception of color by males and females? (671)
The most significant difference is in terms of color blindness. Color blindness is a sex-linked genetic trait that is carried by women and normally expressed in men. So while about 8% of males have some form of color vision deficiency, there are almost no females with color vision deficiencies. There are a few other differences, but they seem to have little meaningful impact on perception. For example, it is possible for a woman to have 4 types of cone receptors instead of the "normal" three. However, there is no evidence that they make any special use of them. Their color vision is still trichromatic (3 dimensional) and the fourth type is very similar to one of the others anyway. (Back to top)


What trends are typical when Munsell testing a group of people? Are there effects due to age, gender, education, or ethnicity? (668)
I haven't noticed anything systematic like that in our testing over the years, but we haven't looked for such effects either. You might inquire with the folks at GretagMacbeth about whether there are data on such effects (much of this sort of thing is described in the manual that accompanies the tests). I've never seen data on age vs. results, but as people age their lens yellows, so that would suggest that the blue colors would become harder to discriminate with age. However, a little more light in the blue end of the spectrum might counteract that effect. That brings me to one thought on your results. You might be seeing a systematic trend to more errors in the blue due to some aspect of your viewing conditions being different from normal (e.g., maybe your daylight sources are at a lower correlated color temperature or the luminance is low). There are definitely more errors at lower luminance levels. There should be no correlation with ethnicity or education, but there can certainly be a correlation with motivation. Could it be that your observed correlations are really correlations with some other variable, like motivation to perform the test. If one is not interested in it, they can have wonderful color vision and still score quite poorly. (Back to top)


What color do most people answer when asked to name a color quickly? (665)
I am not aware of any research on that specific question, although some might exist. This website suggests that the answer might be "red" since it is usually the first color name to evolve in a language after black and white. That makes some sense and is based on classic work on categorical color naming by Berlin and Kay. Another reasonable guess might be "blue" since that tends to be the most popular "favorite" color. You might also look into the research in this paper (Boynton, R. M. and Olson, C. X. (1987) Locating Basic Colors in the OSA Space, Color Research and Application, 12, 2, pp. 94-105.) in which people were asked to name colors as quickly as they could and people were quicker and more consistent when the using Berlin and Kay's eleven basic color terms. (Back to top)


Is there any standard by which Munsell colors are called "light" or "dark" or are those terms that are too subjective so that they don't get used? (663)
I'd suggest that you take a look at the "ISCC-NBS Dictionary of Color Names" for the most systematic relationship between Munsell designations and common color names. It is out of print, but can often be found from used book sellers and in libraries. Also, to clarify, in Munsell Value 0 is perfect black, Value 10 perfect white, and Value 5 a middle gray perceived to be halfway between white and black. Thus anything above Value 5 would be a light gray until it is called white (maybe above Value 8 or so) and anything below Value 5 is a dark gray until it is called black (maybe below Value 2 or so). (Back to top)


Can you comment on how does the following colors affect human psychology when considered in relation to fashion designing: red, yellow, blue, green, orange, violet, brown, pink, white, black, grey? (660)
The psychological/emotional effects of color in any context (fashion design or other) are not really that systematic and precise. There is no question that there are psychological responses to color, but they are very individual and come from different learning situations (e.g., society, personal experiences, etc.). You will probably be able to find books that give you whatever answer you want for the colors you listed. I'd recommend taking a look at Faber Birren's "Color and Human Response" to get a well-written and technically-balanced summary of these types of effects. (Back to top)


Are there any filters that can be placed over the eyes to make a substance, which is invisible to the naked eye, visible through the filter? Can you give an example? (659)
Sure, there are plenty. For example you could print a fine pattern in yellow on a white background that would be normally invisible and then view the object through a blue filter which would make the yellow areas very dark. My daughter has a game that has hidden answers unless you look through a red filter. The text is cyan on a white background with a high-frequency red masking pattern on top of it. The red filter makes the white and red match (the masking pattern goes away) and the text becomes plainly visble. You could also use metameric pairs that match for a certain viewing condition. When the viewing condition changes (i.e. you look through the filter), the colors would become discriminable. Lastly, you could use a fluorescent material and then changes in either the illumination, or the illumination with filtration could make the material visible. (Back to top)


Is there a range of Munsell or L*C*h coordinates that would describe browns? (657)
Yes, there is a range, but I don't know of a strict definition. I would recommend a very interesting paper on the topic (CJ Bartleson, Brown, Color Res. Appl. 1, 181-191 (1976)) that includes scaling of brown and defines the boundaries of brown in Munsell space. You could also just have a few people look at samples and estimate boundaries yourself. You might also take a look at the "ISCC-NBS Dictionary of Color Names." It is out of print, but an internet search may find copies. (Back to top)


What color is best to paint a room with hardwood floors to enhance productiivity? (654)
There are plenty of theories on these sorts of things, but very little hard science. I would say that the best color is one that makes you comfortable and keeps the room fairly bright (but not uncomfortably so). When there is more light, you see better, there is less eye strain, etc. and all of that should make you more productive. It also saves energy since lighter paint will reflect more light and require less output from your lamps. (Back to top)


I am looking for products to protect my eyes from UV-C light (254 nm). What substances are opaque or reflect to UV-C light? How harmful is UV-C light to human skin and eyes? Can you suggest any protective measures I should take? (652)
I did a google search on "UVC Safety" and found many products and a lot of information. UVC is extremely harmful radiation, so you should be careful with it and take every possible precaution. In nature, it is absorbed by the atmosphere and does not reach the Earth's surface. In human hands it is used to do things like kill bacteria because it is so good at destroying biological tissue. Apparently it can even cause changes in DNA structure. Here is a link to a document that outlines some safety procedures. Good luck with your work and be careful; protect both your eyes and your skin. (Back to top)


Is there a certain color that has been proven to be least tiring to the eye on web page backgrounds? (649)
I don't know if any research has been done on web pages specifically, but it is well established that dark text on a white background is least fatiguing for extended amounts of reading. That's why most computer systems arrange the text that way. For presentations in a darkened room (and short amounts of text), bright text on a dark background is easiest to read. (Back to top)


Why can't humans see colors that fall in the UV or IR part of the electromagnetic spectrum? (647)
It is difficult to answer briefly, but it has to do with the visible range of wavelengths being were a lot of the important information about our world is and with the reactions of biological tissue to electromagnetic energy. UV is damaging to tissue and is best absorbed to protect us rather than being used in our visual system. IR is also produced emitted by warm objects, like our bodies, and it is difficult to overcome this background emission (noise) to detect IR signals in the world. (Back to top)


How often should color vision testing be assessed if the ability to see colors is important in one's occupation? (642)
Most color vision deficiencies are acquired and do not change through our lifetime. For those cases, once is enough to diagnose the presence or absence of a color vision deficiency. If you are interested in color discrimination ability (e.g. some of the information given by the Farnsworth-Munsell 100-Hue Test), then that can change with both age and motivation. I would suggest that doing that exam once every two years or so would be more than adequate. (As a note, I have done the test for more than 20 years and my results have not significantly changed when I am motivated to do the exam carefully.) (Back to top)


Can chromatic discrimination change over time or can it improve through practice? (640)
It can certainly change over time, but I am not aware of any data that suggest an improvement with practice. What might improve with practice is the awareness of certain attributes or the motivation to be concerned with the differences. The raw color discrimination capability doesn't improve with practice, just the ability to do related tasks. (Back to top)


Any correlation between age and chromatic discrimination ability? (639)
In general, as we age our color discrimination ability decreases (except for young infants where it is still improving). This is largely due to the gradual yellowing of the lens in our eyes, which also results in more scattering and reduced luminance sensitivity. (Back to top)


Do any illnesses/physical characteristics/disabilities impact one's chromatic discrimination ability? (638)
I have heard of illnesses or various other injuries impacting chromatic discrimination. For example, there are cases of tumors in certain locations in the brain that cause the patient to have achromatic perception (a black and white world). I don't know much about details, but it is possible. (Back to top)


How can a color display with three monochromatic lasers produce a finely rendered colorspace, with what seem like the appropriate pastels and everything? (637)
This is because our eyes cannot tell how a stimulus is made. We have three types of cones in our retinas and as long as the energy absorbed in the three types is equal for two stimuli (e.g. a pastel made with paint and illuminated with daylight vs. a pastel made with three lasers, then the colors will match. This is the definition of metamerism, which is the basis of modern colorimetry. (Back to top)


What are the different textures of colour? (636)
Texture is usually considered separate from color as the spatial distribution of colors, the spatial distribution of gloss, or the spatial distribution of the surface height of the object. Color is normally treated as a distinct measurable value (a perception). (Back to top)


How do the eye and the brain work together to create the chromatic adaptation 'illusion' effect with colours? Also, why does looking at certain stimulus for certain lengths of time effect the time span of the adaptation? (632)
Here's a nice little demo of chromatic adaptation .

To try to answer your question. The eye accomplishes chromatic adaptation through adjustment of the sensitivity of the three types of cone receptors based on their previous exposure to light (more exposed to blue, the receptors become less sensitive to blue). This is like an automatic exposure control (or more precisely and automatic white balance) in a digital camera or camcorder. The brain helps by interpreting the world and discounting illumination effects (such as shadows or clearly colored light sources) to help us better recognize objects (which are usually more interesting to us than illumination). This is called "discounting-the-illuminant" and is essentially a sub-conscious cognitive effect (it can be learned and unlearned in certain situations ... normally in the form of illusions).

The time-course of chromatic adaptation is not really dependent on the stimulus. It is essentially complete in about two minutes. However, often when looking at adaptation effects, we don't take the time to fully adapt and the illusion, or after-effect, goes away in roughly the same amount of time we took to adapt. There are some higher-level after-effects that can take longer to go away. You might search on the "McCullough Effect" to learn about one of those. (Back to top)


Is there any research on changing the colors of a light to improve a surgeons abilility to see in different surgical enviroments? Can you improve their contrast sensitivity like skiers do with colored lenses. (625)
I am not aware of any research on this topic and couldn't find any in a brief internet search. It seems the main concerns in surgical lighting are the elimination of shadows, high luminance (improving acuity and color discrimination), and white (best for rendering all colors). A specific color other than white might be helpful for certain types of surgery (depending on the colors of the features being operated on), but it would also change the appearance of everything else and that might make it less comfortable/familiar for the surgeon. (Back to top)


What is the problem if a person sees both gold and silver as silver? This person also has red-green defects. (617)
Since you mention that the person has a red-green deficiency, that really answers the question. A red-green deficiency can be consistent with a confusion of silver and gold. Although it would depend on the illumination, the discrimination between silver and gold (which is a color discrimination) could well fall along a line of confusion for a person with red-green color blindness. You might take an image with silver and gold in it and process it through the tools at vischeck.com. (Back to top)


What is the top that is black and white and makes pale colors when spun? (616)
It's called Benham's top, or Benham's disk. It's easy to find information on it on the internet. Here's an example. (Back to top)


I would like to perform the Farnsworth-Munsell 100 hue test on my monitor. Will this work? Can I have the values of each colour caps to form the colours? (615)
You could, but you would have to be very careful about monitor calibration/characterization, adapting conditions, and luminance level in order for the results to mean anything. It is probably cheaper and easier to simply buy the real test from GretagMacbeth. I don't believe they publish the color definitions, but there might be some academic papers on the topic with data. I would suggest a search in Google Scholar to see if you can find references. (Back to top)


I am writing a story about colour for children. Can you help explain (in simple terms) how a rainbow works and how the mixing of just a few colours in printing pictures in papers works? (601)
I like howstuffworks.com for reasonable explanations of many things. That link is for rainbows and I'm sure they have one on printers, too.

As far as a simple explanation, I just like to say the different colors of light are bent to different angles by the raindrops in the air (for a rainbow). For color printing, you can say that we have only three types of color receptors in our eyes and the primary colors in a printer work to control the responses of those three receptor types. Since there are only three receptors types, only three primaries are required.
<>br> Another good source is the "Magic Schoolbus" books on color and the senses. (Back to top)


How long does it take to perceive color? Are some colors perceived more quickly than others? (599)
It takes about 1/10 of a second to perceive any visual stimulus. But that is the latency for the signal to reach awareness. But the visual system can follow changes, such as flicker, at very fast rates depending on their color and intensity. So even though there is a lag for the signal to reach consciousness, the visual system itself can follow rapid change.

Your question is hard to answer because the answer depends on the state of adaptation of the eye and the intensity of the flash of light. It really doesn't matter how brief a flash of light is if it is bright enough because the response of the eye is accumulated over time.

But it is safe to say that under certain certain laboratory conditions, one can show that red and green are perceived more quickly than blue and yellow and that white/black differences are the fastest. But under normal viewing conditions, these differences will not be observed. (Back to top)


Do people with light colored eyes have better night vision than people with dark colored eyes? (590)
I don't believe there are any data to suggest that eye color has a significant systematic effect on visual performance. (Back to top)


When the 3 hands on a spinning toy (which are 3 different sizes, long, medium and short) spin around really fast, they leave 3 "trails" of light in concentric circles. Why do we see 3 complete circles of light all the time? (586)
What a great question! The effect you are seeing is called "Persistence of Vision". A web search on that topic turns up a bunch of good explanations. Here is one experiment about it from the Exploratorium.

Essentially, our eyes take a certain amount of time to respond to stimuli in the world. It is roughly 1/30 of a second. So if your lights make a complete rotation in less than 1/30 sec. then your eyes basically add up all the light for that time period and produce a single image (the circle formed in that time period). It's the same reason that things moving quickly look blurred. You should be able to see similar trails of light by just moving lights around with their hands ... the faster they move the lights, the longer the trails. If they make a full circle quickly enough, then it will appear like a full circle of light. (Back to top)


Do humans have a natural affinity for certain sorts of colors more than others as compared to other creatures? (584)
Our affinity for colors is very much influenced by society, so you could say that we do since our society is different. If there are inherent affinities, then they might well be similar for other animals that have similar visual systems (which turn out to be relatively few in number). (Back to top)


Do insects that have UV sensitivity in their visual system see the UV portion of the spectrum as "color"? (583)
As far as insects, it is really impossible to say for sure, but it seems that there visual systems are designed such that the UV part of the spectrum gets processed as another color response. Of course it is possible that they don't see "color" at all and just use the different responses for different functions (sort of different sets of black and white images for different purposes). (Back to top)


Is color limited to the interaction of light with an object and our eyes? (582)
Yes, we need to have our eyes involved in color but we do a lot of manipulation of lighting and objects to control those color perceptions. So there is plenty of color science that just involves the light and objects without worrying about the eye too much. You need light and the eye, but you don't necessarily need an object ... lights can be colored all on their own. (Back to top)


If no light is falling on an object, does it still technically have a "color"? (581)
Color is technically defined as a perception and if there is no light to initiate that perception, then there is no color. So I would say that if there is no light falling on an object it doesn't have a color. If there is light on other objects in the scene, but none on that one particular object, then its color would be black. (Back to top)


Does the color green inspire thought? (578)
No more so than any other color. Affective responses to color are very real, but they are not consistent from person to person. If green inspires thought in you, that's great, but it might just put someone else to sleep. (Back to top)


How I can mathematically convert from CIELAB (D65,10�) to XYZ (D65,2�) or RGB? (576)
You can't. CIELAB can be converted back to XYZ using the simple inversion of the CIELAB equations, but there is no way to change from the 10� observer to the 2� observer in the process. As far as conversion to RGB, that requires a characterization for the monitor you are using. A common choice is to convert to standard RGB (sRGB) values and there is a set of equations defined for that conversion. (Back to top)


How do the colors you wear affect your appearance? What colors make you look certain ways? (575)
Really, the colors you wear affect your appearance however you believe they do. There are no specific scientific rules that apply in all cases. Some people look and feel good in certain colors, while others will have the same experience in completely different colors. (Back to top)


Why do we recognize uniqueness only for four colors, blue, yellow, green, and red? Is there any color map of unique hues in a visual system? (565)
There seems to be a lot of physiological and psychophysical evidence supporting the special nature of the unique hues in the human visual system. I'd suggest a google scholar search to find lots of interesting references. "Why" is a difficult question, but it is probably related to the nature of the cone photopigment absorptivities and the transformation of them necessarily to maximally decorrelate the spectral signals in the natural world. It is hard to say there is an exact physiological locus for the unique hues, but there are certainly various types of opponent encodings that have been identified and there is certainly a map somewhere in the visual system because the response is such an easily accessible percept. (Back to top)


Why is a red Popsicle red? (563)
Because, in our culture and language, "red" is the name chosen for the color perception generated by that Popsicle. (Back to top)


What is the difference between value and chroma? If I add black or white to a color I am changing its value. How do I change its chroma? (562)
Value (or lightness) refers to the perceptual difference between white (high lightness or value) and black (low lightness). Chroma refers to the difference between a neutral gray (low chroma) and a color of the same lightness that is more colorful (like a vivid red ... a high chroma). Stimuli can, of course, vary in both dimensions at once when physical changes are made. If you add black or white to a color (regardless of what type of color mixing you are doing) you will certainly be changing the value, but you will also be changing chroma. If you want to just change chroma, you should mix the color with a gray of equal lightness. (Back to top)


How does color affect our vision? (547)
Color is our perception that results from vision. So you can't really say that color affects our vision since it is the product of our visual system. Color, in terms of the color of objects or light sources, can affect our visual performance. For example it is easier to read black text on white paper than it is to read yellow text on white paper. There are many ways that color affects visual performance. So many, in fact, that there is no way to give a short answer to this question. (Back to top)


What factors affect the intensity of color? (545)
Many factors influence the intensity of a color. These include the physical properties of the stimulus itself as well as the viewing conditions (color and amount of illumination, surrounding colors, etc.) All of these physical and perceptual factors together determine our perception of color appearance. (Back to top)


Do different people see the same color in different shades? Why? (543)
While normal color vision (that is for observers who are not color blind) is very similar from person to person, there are differences large enough to be noticed. Most often this happens in color matching when one person sees two stimuli as a match and another does not. Simply put, these differences are caused by a number of physiological differences in the visual system (just like people are different in many other ways). Some of the causes are differences in the transmittance of the eye lens (which gets yellow with age and also varies from person to person), a protective yellow filter layer on top of our retinas, and the photoreceptor responses. In addition, there are also differences in the ways individuals assign names to various colors. (Back to top)


How does one resolve the concepts of the 'scientific' (linear) color frequency model and the 'artistic' (circular) color wheel model in regards to color perception? (542)
The resolution is quite simple and close to what you suggested:

[the rest of the question, in the questioner's words] "If we look at a color wheel and assign a corresponding light frequency to each point on the wheel, high frequency blue around to low frequency red, it seems that somewhere in 'purple/violet' range that there would be a point which represents both the very highest perceptible color frequency and the very lowest!?"

The linear representation of color is in fact simply a representation of the physical stimulus in terms of wavelenght (or frequency). This does help define the stimulus, but not the color perceptions. To fully describe color in a scientific way, one must factor in the the human visual system. Once this is done, systems of colorimetry easily represent the circular nature of hue by connecting mixtures of the two ends of the spectrum to produce purples. So both scientists and artists describe the perception of hue as circular. (Back to top)


I am a member of an internet forum dedicated to the Rubik's cube. What is the set of 6 colors (including black/white) that human eye is best able to discriminate? (538)
Generally research on color contrast involves only two colors (such as text on a background), so this is definitely an interesting question. You have already identified black and white and they should certainly be included in your set of six. The next step would be to include 4 chromatic colors that are of intermediate lightness (i.e., not very dark or very light so that they are not easily confused with the white or black). While it is difficult to say what the optimum choices would be, there is probably very little to gain in performance once the colors are separated into distinct hue categories that would not be confused. For example, choosing yellow, green, blue, and red would be about as good as you can do. You just want to make sure that the blue and green are clearly distinguishable which might be accomplished best by making the blue slightly purplish. (Back to top)


I am a competitive rifle shooter. Are there any colored filters to place in my rifle sight that would help to reduce eye fatigue or even simply aid in aligning things? (536)
The best answer will probably vary a bit from person to person and with the particular details of the lighting. However, a good general rule for both the outdoor and indoor situations would be to use a yellow filter (or something similar). The yellow filters will remove short-wavelength (blue) light that is most detrimental to your visual acuity for many reasons. The blue light is scattered the most in the environment and in your visual system and thus produces the most flare that reduces the contrast of objects. Also, your visual system has very poor acuity for blue light (try reading blue text on a black background or yellow text on a white background, which is detected by the difference in the blue light, to see how poor your blue vision is) because of chromatic aberration in your eye and because of the distribution of different photoreceptor types. So looking through a yellow filter will give you the best contrast and acuity in general. You might be able to fine tune this a little bit for individual observers, objects (targets), and lighting. I'd suggest trying a range of yellowish filters and choosing the one that is most comfortable for you and produces the best results. Good luck with your training for the Olympics and I hope this was helpful. (Back to top)


What distance can humans still distinguish between different colors? (534)
There are a couple of areas for you to explore further. One is called "small-area tritanopia." That refers to the fact that the central area of our fovea has no blue-sensitive cones and our vision for small objects (less than 0.25 degree or so) becomes tritanopic (yellow-blue) color blind. The second are the "chromatic contrast sensitivity functions." These provide data, like those you cited for acuity. Unfortunately the results depend very much on the definition of chromatic contrast and the viewing conditions. As a very rough estimate, you could assume that the ability to discriminate colors has about half the acuity of our ability to see the objects. So, roughly speaking, if you can just see the 2.5m object at 1700m, it would probably have to be 5m in size to reliably distinguish colors. (Back to top)


Is black paint recommend for a boy's bedroom? (532)
First of all, whether the child is a boy or girl makes no difference. Black is an unusual choice for room paint, but if it is the child's preference and it is not related to any other behavior you want to discourage, then there should be no problem. There are two reasons to avoid black paint though. First the room will be very dark and it will take more lighting (and therefore more energy) to illuminate it to the level needed to do homework, etc. (White walls are very energy efficient since they reflect almost all the light and higher levels of illumination can be obtained with fewer lighting fixtures.) Second, when it comes time to paint the room again it will be more difficult to effectively cover the black paint (more coats of new paint required). White, on the other hand, is very easy to cover. (Back to top)


Why are common soccer balls black and white? (528)
I don't know the answer for sure, but I would guess that the black and white pattern makes them easiest to see against a variety of backgrounds and when moving quickly. This because black and white have the most visual contrast. I also found this web site with a more extensive explanation. (Back to top)


Is it possible to make a color that is not visible to the human eye? (524)
No. The definition of color specifies that it is an attribute of visual sensation. If there is no visual sensation, then there is no color. (Back to top)


Do age and gender matter when seeing color? (523)
There are some gender-dependent differences in color vision, but not of general significance. The most significant being that color vision deficiencies are far more common in males than females (usually a sex-linked genetic trait). With respect to age, there are differences due to the natural yellowing of our lens as we age. However, these differences are also relatively small when compared to the variation from individual to individual at any given age. (Back to top)


What hue can the human eye dicern the most shades of? (518)
This question is impossible to answer definitively, which is why you find conflicting answers. The answer will depend on how one defines hue, the type of stimuli, and the viewing conditions. If forced to give an answer, I would select purple. I base that on the structure of a color space in which perceptual hue differences are equally spaced around the hue circle. In such a space, the greatest area is devoted to hues that would be called purple. That indicates that we can perceive the most distinct hue differences in what we would call purple.

Please note however, that with other definitions of the visual task and viewing conditions it is quite possible to derive and defend other answers. I'm sorry I can't give a single, definitive answer, but I do hope this helps you understand the difficulties in exploring this topic. (Back to top)


Can the brain take a 2D image (eg: a picture) and convert it to a 3D image? (506)
Yes! Our visual system (of which the brain is a key part) is capable of fairly accurately computing 3D geometry from 2D images. There are times it will be tricked, or there won't be enough information available in the 2D image, but generally (especially if there is motion, or multiple views) we can do quite well. Often what are called visual illusions are stimuli designed to trick our visual systems into making an "incorrect" interpretation. There is much research on topics like "shape from shading", "shape from motion", etc. that describe how we use the clues available in an image to compute 3D geometry. (Back to top)


Can you tell me what color eye shadow would look the best for a given complexion? (503)
This really isn't a question of science, but one of preference. A color you like might look quite distasteful to others, etc. There is one perceptual phenomenon that might guide you little. An effect known as "spreading" causes perceived colors to be enhanced by similar colors that are nearby. That would suggest that to enhance your eye color, you might want to consider eye shadow of similar color. Strangely enough, the effect reverses itself when the colors being viewed are larger, but since your eyes are normally viewed from some distance, the spreading effect probably does come into play most of the time. Of course other criteria might also be important in deciding the colors for cosmetics, so ultimately you need to do what you like. (Back to top)


Do different colors affect your eye sight different over time? (501)
No. As long as you avoid extremes, like staring directly at the sun, and view a variety of colors, then your visual system will not be affected. Lack of variety in exposure to color can produce long-term adaptation. For example, if you always wore red lenses, your visual system would adapt over the long term to be less sensitive to red. However, this effect is reversible. (Back to top)


What is the real meaning of color blind? (498)
In the vast majority of cases, "color blind" refers to people who have a deficiency in their color vision. In fact, "color vision deficiency" is a more appropriate term. People with deficiencies generally confuse certain hues. For example most have some form of red-green confusion while others exhibit a yellow-blue confusion. There are very rare cases of people with monochromatic vision who can only see in shades of gray (they confuse all hues). There is more information in this answer. (Back to top)


Did humans use chromatic adaptation long ago, for example in hunting? (497)
The apparent advantage of chromatic adaptation is that it helps humans (and other animals) to reliably identify objects across significant changes in the color and intensity of light sources. These changes happen with natural illumination (daylight is very yellowish in the morning and evening and bluish at mid-day and also changes color significantly with weather conditions) as well as more modern artificial illumination. Chromatic adaptation to natural variations in daylight is very helpful for activities like hunting, gathering food, and protection from predators. There's really no doubt that the visual systems of humans (and other animals) have been taking advantage of chromatic adaptation for a very long time. (Back to top)


Does the color of your eyes affect your vision? Do people with blue eyes have better vision than those with green? (496)
I have never heard of any research to suggest that the quality of your vision (for either acuity or color) is affected by eye color. While theoretically, it might be possible for their to be some effect, other variables in our visual system are almost certain to overwhelm any variability due to eye color. So the short answer is "no". (Back to top)


Do you know of any table of rgb value pairs that make up visual complementaries (colors that are afterimage of each other)? (494)
I am not aware of any such tables and it would be difficult to construct one since RGB values are device dependent and a pair of RGBs that would be afterimage complementaries on one display might well not be on a second display. There is also significant inter-observer variability (and difficulty in judging the colors of afterimages) that would complicate matters. Sets that you construct yourself are likely to be just about as good as those constructed by anyone else. (And would certainly be better for your visual system and your display.) (Back to top)


How does color affect our mood? (489)
There is no question that color can affect our mood, but there is no specific relationship between particular colors and moods. A color that affects one person one way might affect another a different way, or not at all. I'd recommend Faber Birren's book, "Color & Human Response" as a good starting point if you are interested in learning more about this and related topics. (Back to top)


I need an example or a graph help to explain why humans cannot see colors that fall in the ultraviolet or infrared part of the electromagnetic spectrum. (483)
This web page seems to illustrate it fairly well. I would also recommend the first chapter of Berns' book, "Principles of Color Technology, 3rd Ed." (Back to top)


How does the eye see colors that are moving very rapidly? (eg: a spinning color wheel) (479)
I am assuming you mean a color wheel made up of several colored segments that spins rapidly and appears as a single color. That is called a Maxwell disk. Maxwell used such a device to study how the human visual system perceives color and determined that all colors can be matched by additive combinations of three primaries. What happens is that the disk is spinning so quickly that we are no longer able to resolve the individual segments and they blur together. The color effect is the same as superimposing three projected lights and is known as additive color mixing. There is a good explanation/description at www.handprint.com. Another way colors are produced with spinning disks is by using black-and-white patterns that result in different stimulation of the three cone types in our eyes and thus produce colors where there physically are none. That demonstration is known as Benham's disk (as well as other names). A demonstration is described at exploratorium.edu. Web searches on either of these topics will turn up a lot of good demonstrations and explanations. (Back to top)


Which colour has the most easily visually discriminable levels of saturation? The literature seems to suggest blue violet as this has the most steps when white light is added in 'just noticeable' amounts - would you agree with this? (473)
This is a difficult question to answer precisely since there are multiple ways that saturation could be defined. The definition you mention, number of perceivable steps between an additive mixture of white and a spectral color does suggest that the violet region is the "best". This, as you mentioned, has been reported in the literature and also seems to be consistent with object-color perception (although that adds many other complications in defining the "maximum" saturation.) The historical literature on this topic is reviewed in section 7.10.3 of Wyszecki and Stiles "Color Science" (in case you haven't already looked there). (Back to top)


Does the first color you see when you wake up effect your mood? (468)
Color can influence mood, but not in the same way for everyone. So I would say that it is possible that the first color you see could influence mood (although probably not consistently in most cases), but that it doesn't necessarily do so. Probably, for most people, the first color has little or no influence on its own. (Back to top)


Do you think people can remember words better from colored paper or white paper? (466)
Text and/or paper of various colors will certainly influence the legibility of words. However, once the word is read I would suspect that the color of the paper would have no influence on how well it is remembered. (Back to top)


I would like to do a science experiment on "Will male and females chose the color that has been associated with their gender?" For example, pink for girls and blue for boys. Can you help be to create a 5th grade science experiment to test this idea? (465)
An important question to consider will be the context of the question. For example, you would likely get one answer if you just ask people to rank their favorite colors from a set and another if those colors are associated with some particular object (like a doll or other toy) or application (like paint for your bedroom wall or clothing). I'd suggest selecting a range of colors and then asking people to select their favorite both when the colors are simple patches (like pieces of paper) and when they are associated with specific objects or uses. Then you can examine the frequency that each color is selected for males and females (and perhaps see if there is an influence of age) for each question. I would also include a range of colors, not just pink and blue. (Back to top)


Please explain the Bradford Chrmatic adaptation transform as a physical phenomenon and provide the mathematical basis. (457)
The Bradford chromatic adaptation transform is not a physical phenomenon. It is a mathematical model of the process of chromatic adaptation in the human visual system. Essentially, it consists of a 3x3 linear transform from XYZ tristimulus values to an optimized set of RGB responses. These RGB values are then normalized to the RGB values for the illuminant (or chosen white point) using a simple von Kries normalization. One additional twist in the Bradford transformation is that there is an adaptation-dependent exponential nonlinearity on the B channel (while the R and G channels remain strictly linear). A modified form of the Bradford chromatic adaptation transform was used in the CIECAM97s color appearance model. Details on both can be found in "Color Appearance Models, 2nd Ed." by Fairchild. (Back to top)


Can human eyes see noise? Or, can our brain recognize what's signal and what's noise? (451)
Yes, the human visual system can see and perceive noise, both noise internal to the visual system itself and noise present in stimuli. We have no problem recognizing signal from noise in most situations. Keep in mind that "signal" is often defined simply as the part of the stimulus we are interested in. (Back to top)


What would be the ideal color for drafting rooms or any rooms used by art students? (444)
Really, the ideal color is one that makes the students most comfortable and therefore able to focus on their work. However, that answer is likely to vary significantly from person to person. From a color science and perception perspective the best color would be a neutral gray and generally a light gray is preferable. The reason for this is that the gray will not bias color perception for any other colors being viewed or used in the artwork. This is why standard color viewing booths have a light gray interior. However, making a room completely gray might be a little too drab and cause students to not enjoy being in the room. So a little bit of color in the room is probably helpful. It's probably best to just avoid an overall bias toward a single highly chromatic hue. (Back to top)


Is there something like color adaptation? I was wearing a blue light filter over one eye and felt that the differnce in color perception between the right and left eye disappeared after some time. When removing the filter, color perception in the previously uncovered eye felt like wearing a blue light filter for a short period of time. (436)
Yes! There is color adaptation, but it is typically referred to as "chromatic adaptation". Chromatic adaptation allows your visual system to adjust for overall changes in the color of the illumination so that objects approximately retain their color appearance. Putting filters over your eyes has the same effect as changing the color of the lighting. Since much of the process of chromatic adaptation happens in the retinas of each eye, it is possible to adapt your two eyes to two different colors. That is what you observed when you put a filter over one of your eyes. Once you removed the filter, your eyes still had two different states of adaptation (the previously uncovered eye more adapted to blue or less to yellow) and you observed the same effect as the adaptation between the two eyes became normalized. (Back to top)


If someone walked down the street, what color clothing or facial features would that person have for me to easiest remember him/her? (434)
I think that would depend on the observer somewhat. In general, the most memorable person would be the one that stands out the most. In other words, colors that contrast most with the background and with other people on the street are most likely to be noticed, and therefore remembered. (e.g. If everyone is wearing gray, then the one person in red might be best remembered. However, if everyone is wearing red, then the one person in gray will be the one to stand out.) (Back to top)


Does age and sex determine what color car a person buys? (433)
Not to my knowledge in any set physiological way. However, societal/cultural norms and trends will always influence preferences, which in turn influence purchasing decisions. Also the manufacturers dictate these choices to a degree by the colors that they make available for the various models. (Back to top)


I am doing a science project on what colors are easiest to see in the dark. Can you help me figure out what experiment I should do? (431)
There are a variety of experiments you could do. I would suggest two things to consider. One is the visibility of the colors in comparison to how visible they are in daylight illumination and the second is contrast of the colors with their background (really that is the definition of visibility). For example, you could select several different hues (say red, green, yellow, and blue ... more if you like) that look like they are equally bright under daylight illumination to use in the experiment. Construction paper or paint samples from a hardware store make good inexpensive color samples. You would then want to compare their visibility in the dark to that in daylight. This is where contrast comes in. Some colors will be more visible against a black background and others against a white background. It would be interesting to try all the colors on each background. If you mount the different colors on white and black backgrounds and then view them in a very dark room, I think you will find some interesting results regarding which colors are easiest to see. Good luck with the experiment. (Back to top)


How can people distinguish edges of objects? Is this a function of rods or cones, or some organs else? (422)
We detect the presence of edges when the light detected by our rods and cones changes abruptly across space (location on our retina) or time (due to our eyes moving). These changes in light intensity are what produce the signals ultimately transmitted to our brains and interpreted as objects (defined by their edges). So, yes, it is a function of our rods and cones with our cones being a little bit better at it than rods. (Back to top)


On what things color depend so that only some colors disappear while others remain? (419)
To quote the CIE, "perceived color depends on the spectral distribution of the colour stimulus, on the size, shape, structure and surround of the stimulus area, on the state of adaptation of the observer's visual system, and on the observer's experience of the prevailing and similar situations of observations." (Back to top)


Where can I buy Baker-Miller Pink? (417)
I am not aware of any specific supplier of Baker-Miller Pink. Previously it was believed that only a certain shade of pink had the desired effect. Further research showed that the effect was short-lived and, in some cases, the pink could cause more distress upon prolonged exposure. I suspect that's why there aren't specific suppliers of paint in that color. This web page provides some information. Some say it is the pink of Pepto-Bismol. If you really want some paint that color, I would suggest looking at paint chips to pick the one closest to the desired color, or finding another material in the desired color and taking that to a paint store to be matched. (Back to top)


Will we ever be able to see colours we have never have seen? When I tell other people about my wonder to have different perceptions they think it is bogus. Will genetics and medicine make it possible in the future? When? (414)
This is a fascinating question. Essentially, in order to have different color perceptions we would need to have a different visual system. That could mean photoreceptors sensitive to different wavelengths or different types of photoreceptors and processing sensitive to the same visible regions of wavelength. There are certainly examples of animals that have very different color responses (e.g. birds and insects), so it is physiologically possible. There would have to be some evolutionary advantage for such capabilities to develop in humans and it is probably unlikely such changes would happen anytime soon. However, you never know.

There are certainly examples of medication that can give us illusions and perceptions beyond normal experience, but probably not with the control required to give us meaningful new color perception capabilities. Of course there is always technology and imaging systems such as infrared, x-ray, etc. give us ways to extend our visual system's capability right now.

If you are curious about possible differences in human color vision, do a web search on "tetrachromatic females" and explore the results a bit. (Back to top)


Why is it more difficult to say the color of the word when it is printed in a different color? (413)
This is known as the Stroop Effect. An internet search on "Stroop Effect" will turn up plenty of examples and explanations. This page aculty.washington.edu has an interactive experiment and explanation. Briefly, the effect is due to interference between your perception of the words and the colors of the letters. Apparently the words are either processed more quickly or more easily in our brains than the colors are. (Back to top)


How do I measure contrast? (402)
Contrast is normally measured using the luminance dimension of color (the Y tristimulus value) or a transform of that to better predict perceived lightness (L* in the CIELAB space). Generally, regardless of color, the greatest visibility is when there is the most luminance (or lightness) contrast. The point at which contrast can be noticed is a determination of the contrast threshold. Much has been published on contrast thresholds and there is no simple answer. The amount of contrast required for detection depends on the configuration (size, shape, flicker, etc.) of the stimulus. In the best cases, it can be as low as a .1% change in luminance. In other cases it might require 10% or more. Unfortunately I can't give you a simple answer. In terms of CIELAB L*, people generally say that a difference of 1.0-2.0 units is just perceptible for relatively large stimuli. (Back to top)


What are "suprathresholds" and "thresholds," with reference to color difference? (399)
"Suprathreshold" refers to stimuli that are clearly visible. In the case of color differences, it would refer to a pair of stimuli in which the difference was clearly perceptible. "Threshold" on the other hand refers to color differences that are just barely perceptible. The magnitude of a color-difference threshold depends on details of the viewing conditions, stimulus configuration, and color in question. (Back to top)


I want to see what make-up shades and colours suit which skin tone, for a school project. Please get back to me with a colour wheel and and some useful information. (384)
I'm afraid this is outside the normal realm of color science. Proper cosmetics colors for various skin tones are a matter of personal preference and a variety of opinions. I would suggest that you look at some of the tips and ideas that can be found on the websites of various cosmetics manufacturers. Sorry I can't be more specific. (Back to top)


Why does the spinning Benham top look colored? Is there any simple explanation of that phenomenon? (379)
There is not a simple explanation for the colors observed. Clearly they are based on some mechanisms in the visual system responding at different temporal rates, but the correlation with the patterns and simple assumptions about the rate of cone responses is not easily shown. The color probably depend on differences in higher level visual mechanisms as well. There is a short discussion with links here. (Back to top)


People of my area prefer reddish black on textiles. What kind of black do people in your area prefer on textiles? (369)
I have heard of people preferring either warm (reddish) or cool (bluish) blacks in various situations. However, I am not aware of any specific trend in that preference based on geography or application. At least in my experience, it seems that the preference depends on the person and situation. (Back to top)


Where can one buy an anomaloscope? Does an instrument exist that has a bipartite field like an anomaloscope but allows any combination of one or two monochromatic lights in each half of the field? (366)
It seems that most researchers end up building one themselves on an optical table. This would probably end up being more cost effective and flexible (given your desire for multiple wavelengths) than purchasing a commercial instrument. There are a couple available that we found with a web search. (Back to top)


What is colour? How is it detected? (365)
According to the official CIE definition in the International Lighting Vocabulary, color is an "attribute of visual perception consisting of any combination of chromatic and achromatic content. This attribute can be described by chromatic color names such as yellow, orange, brown, red, pink, green, blue, purple, etc., or by achromatic color names such as white, gray, black, etc., and qualified by bright, dim, light, dark, etc., or by combinations of such names. Perceived color depends on the spectral distribution of the color stimulus, on the size, shape, structure, and surround of the stimulus area, on the state of adaptation of the observer s visual system, and on the observer s experience of the prevailing and similar situations of observations."

Color is detected by the human visual system. The physical attributes of light and objects that produce the stimulus for color are measured with spectroradiometers and spectrophotometers. Correlates of our color perceptions are then computed from those physical measurements using the CIE system of colorimetry. (Back to top)


Is it true that only some dreams are in color, while others are in shades of gray? (356)
Yes. I regularly experience both black-and-white and color dreams. There has been folklore that people only dreamed in black and white, but that appears to be the result of poor dream recall and cultural influences. There are some interesting references on this page on the topic. Some say that all dreams are in color, but we sometimes don't remember the color. Since we experience black and white images both in natural settings (as in low luminance levels where we lose color vision) and through technology (black and white photographs and video), there is no reason to believe we couldn't replicate that perceptual experience in a dream. (Back to top)


Sign language interpreters have always been taught that they should wear colors that are in contrast to their skin tone to create maximum visibility and minimize eye fatique. Is there a more scientific way to teach these principles? What does research tell us about clothing color and eye fatique? (355)
It makes perfect sense to have maximum contrast between the hand color and the background clothing. This will make the hands themselves and movements of the hands easiest to perceive. That is true of any object, printed text, etc. I have never heard of research on particular clothing colors and eye fatigue, but there is no question that lower lightness contrast (i.e. clothing that is not significantly lighter or darker than the hands) will be harder on the eyes. The scientific way to teach these principles would be to explain the idea of lightness and contrast between the background an object of interest. Here is a web page that talks about it for text. The principles would be the same for the perception of anything else. (Back to top)


Somedays my eyes look green and other days they look more blue. What color of clothing or eye shadow would I wear to make them appear more green? What colors should I NOT wear if I don't want them to look blue? (352)
The changing colors of your eyes might well have more to do with changes in the color of the illumination than in your choices of eye shadow or clothing. Your eye shadow will probably enhance eye color through simultaneous contrast (since your eyelids are close to your iris - the colored part of your eye). In that case you want to choose colors that are additive complementaries to the green (that would be things like purple, pink, magenta). More yellowish eye shadow colors (like gold or orange) would serve to make your eyes look more bluish. As far as clothing, I have read that choosing clothes similar in color to the eyes helps people notice the eye color through some kind of grouping Gestalt. That makes sense since the clothes are too far away for simultaneous contrast. Thus, where green to bring out the green eyes and avoid blue.

Most of all, I would encourage you to pay attention to the lighting. It might be that your eyes look more green under inside (incandescent) lighting and more blue under daylight. That might be the more important issue. (Back to top)


I am testing whether colored (red and blue) backgrounds enhance or detract from a person's ability to assemble puzzles. Have these experiments like this have been done before? Any idea which age groups to test? (345)
I have recently heard of some research that showed that people exposed briefly to red (as opposed to green) before an IQ test did not perform as well. Apparently the red exposure produces a kind of avoidance response that might also happen for other tasks such as sporting events, or in your case, assembling puzzles. Given those results, I wouldn't be surprised if you find something significant in your experiment. That work has not been published yet and I don't think there is a lot similar to what you are planning. I don't have any insight into the best age groups, but would expect that any result would generalize across ages. Keep in mind that there will be individual variation. Red might be faster for one person and slower for another. However, when you average across enough people you might see a significant result. (Back to top)


Blue colors wouldn't have to have higher UV reflectance than other colors and I am sure exceptions can be found. However, in general blue objects are reflecting highly in the short-wavelength end of the spectrum and that reflectance continues into the UV. Another way to look at it is that the wavelengths they tend to absorb are mainly longer than the the blue and UV wavelengths while other colors are largely absorbing the shorter wavelengths. (342)
There really are not any well established rules with respect to color and it's effect on people. Color certainly has psychological effects, but they vary substantially from person to person. The best bet is to make sure that the brochures are pleasant and legible. Following basic rules of good design, including harmonious use of color will probably serve you best.

You might also inquire with the Color Marketing Group to see if they have any guidelines or suggestions. (Back to top)


Has research been done to determine how closely the color receptors in various species match what one might expect given their evolutionary environment? (335)
This is a fascinating question. Essentially the answer is "yes." There are a couple of classic vision papers that address the issue. One is H.B. Barlow, "What causes trichromacy? A theoretical analysis using comb-filtered spectra," Vision Research 22, 635-643 (1982). Barlow shows that the the spectral frequency content in typical color stimuli is adequately sampled with 3 band-limited mechanisms similar to cone responsivities. The second is G. Buchsbaum & A. Gottschalk, "Trichromacy, opponent colours coding and optimum colour information transmission in the retina," Proceedings of the Royal Society (London), B220:89-113 (1983). They show that opponent channels optimally encode visual information. A more recent reference on the topic is T.-W. Lee, T. Wachtler, and T.J. Sejnowski, "Color opponency is an efficient representation of spectral properties of natural scenes," Vision Research 42, 2095-2103 (2002). (Back to top)


When driving at night, what colors on cars are easier to see and what colors are harder to see? (333)
At night, your rod system often becomes more important than your cone system for seeing objects. The rods are sensitive to shorter wavelengths than the cones. (This is why red objects tend to look black at night, the rods simply don't respond to red light.) The easiest things to see are those that contrast most with the background. Assuming the background is dark, you want cars that would appear light. White will always be a good choice for this since it is lighter than the background for both rods (when no extra light is on the car) and cones (when headlights are shining on it). As far as chromatic colors, a light blue would probably be then next best choice. As I mentioned above, red would not be good since it would look black to the rod system. A yellow color would probably end up somewhere in between; nice and bright for the cones, but a bit darker for the rods. (Back to top)


I want to scan the Ishihara plates and create the same colors on my monitor. Can you help? (331)
First of all, I'm not sure the publisher of the Ishihara plates really wants you to be doing this. You should check into any copyright issues if you are planning more than personal use. Your question is a synopsis of the problem that color management systems are designed to solve. You first need to have your scanner characterized so that the scanned RGB values can be converted to meaningful colorimetric values (like XYZ or CIELAB). This characterization can be embedded in an ICC profile. The characterization must also be created for the lighting under which the plates are properly viewed. Then the same process is completed to characterize the display. Another profile allows conversion from the colorimetric values to the RGB signals required to drive the display to produce the proper colors. You will need to learn more about color management and then purchase a system to profile your scanner and display to complete this task. Berns' "Principles of Color Technology, 3rd Ed." provides some introductory material on color management and there are many other books out there on the topic. (Back to top)


I have a severe color vision deficiency. Can you help me modify images so I can see the world the way others do? (328)
Unfortunately there is no way for you to see the world the way others do. There have been filters, or filter combinations, suggested that would help people with color deficiencies to discriminate the colors they normally cannot (e.g. a different filter on each eye). I am not aware of any of these being particularly successful. There is a little information on that topic in this FAQ . Going the other way, showing others what the world looks like to you (or at least which colors you can't discriminate) is a bit easier. Here is a website that has tools to take images and convert them into versions that illustrate appearance to color deficient observers. There is also a program to help people make images/slides more friendly to those with color deficiencies. It is a very interesting site and the software is technically sound. It might be worthwhile to take some images of your pathology slides through their system to show your colleagues what you are up against. (Back to top)


In performing a mechanical task with several different colored backrounds, which colors would bring the most contrasting results in the efficency of which the task is performed? (315)
Generally objects can be most easily perceived as separate from a background when there is maximal contrast in lightness. In other words, put light objects on a dark background and dark objects on a light background in order to best see the objects. The lightness dimension tends to be more important than the hue and chroma dimensions for the discrimination of objects (especially as they get smaller). There is another effect, known as crispening, that can become important when trying to compare two objects on a background (rather than seeing a single object). I suspect your tasks might involve discriminating difference in objects on a background. In that case, crispening is an effect whereby the apparent differences between objects appears largest when the background is of a color intermediate between the two objects. Thus, if trying to discriminate two middle gray objects, put them on a middle gray background, two dark objects, put them on a dark background, and two light objects, put them on a light background. Also, in general neutral (gray) backgrounds tend to be best overall for viewing a variety of objects and colors. So I'd pick a gray background with lightness about in the middle of the range of the objects that are being manipulated. (Back to top)


What is the best test for screening color vision in employees using penetrant fluorescent dyes to inspect manufactured metal items for defects? (311)
I am not familiar with the specific task involved, but I assume you are interested in measuring your employees' ability to detect and recognize small color changes. Probably the best test for that would be the Farnsworth-Munsell 100-Hue Test. It is a fairly simple to administer test that evaluates color discrimination ability and also screens for color deficiencies. It is currently sold by GretagMacbeth. (Back to top)


What is the best color to paint walls in a machine shop to enchance productivity? (310)
This is an interesting question and I am sure you could find research to support almost any color choice. To be strictly scientific, the only changes that should enhance productivity are those that make the work more visible. That would be light colors. There is an effect known as the "Hawthorne effect" (see wikipedia.org) that suggests what is truly important is the attention given workers. In studies about lighting and wall color, it was found that workers in areas had increased productivity regardless of the changes in their environment. It was the fact that they were put into the special environment that made them happier and more productive. One suggestion is to allow the workers themselves to choose the wall color that they feel would make them more productive. It also seems that changes are important, so maybe asking them to select again every year or two would also help. (Back to top)


If the fovea contains no S cones why don't humans have functional dichromancy in foveal vision? (305)
The visual system is indeed dichromatic for very small stimuli. It is called small-field tritanopia. The key is that most of the fovea does contain S cones. It is only the very central area, less than 0.25 degrees that has no S cones. To observe small-field tritanopia the stimulus must be entirely contained within that small central region of the fovea. Even brief eye movements to areas that will expose the stimulus to S-cones will destroy the effect due to perceptual filling-in (just like the blind spot). (Back to top)


How does the color pink affect the minds of males and females? (302)
Exposure to various colors can have significant and very real physiological and psychological effects on people. However, the rules by which these effects can be predicted are not firm and the effects can be different for different people based on previous experiences, etc. There are many books on the topic, one of the most well-known being "Color and Human Response: Aspects of Light and Color Bearing on the Reactions of Living Things and the Welfare of Human Beings" by Faber Birren. In particular regard to your question about pink, you are probably thinking of Baker Miller Pink, which has been shown to have a calming effect under certain circumstances. There is a good discussion of Baker Miller Pink with some references at colormatters.com. I have not heard of any differences between the reactions of males and females, but it is possible there could be some psychological differences due to cultural conditioning. It has been suggested that Benjamin Moore's Deco Rose #1328 closely matches the historically used shade of pink. (Back to top)


Is there any standard Colorimetric values of this GSC (Gray-Scale Comparison Method) method used for visual assessment was used by Luo and Rigg? (296)
The technique is general and there are no specific requirements or standards for the gray samples used as references. (Back to top)


What's the minimum Δfreq or Δwavelength an average person can differentiate so as to recognize two different colors? (291)
Our ability to perceive changes in wavelength depends on several variables, most important of which are the wavelength itself and the luminance level. As a general rule of thumb, it is reasonable to say that we are able to detect changes in wavelength of about 2nm in the middle of the visible spectrum. At the ends of the spectrum this number increases and it becomes undefined at the very ends of the visible spectrum where only a single type of cone photoreceptor is responding to the stimulus. Some classic measurements of wavelength discrimination are given in Wyszecki and Stiles, Color Science, 2nd Ed. on pages 570 and 571. The show, among others, results from a 1934 study by Wright and Pitt indicating that wavelength discrimination was as good as about 1nm near 500 and 600nm, around 2nm for much of the visible spectrum and then in excess of 5nm for wavelengths below 430nm and above 650nm. (Back to top)


Why do we have color vision, and what is the evolutionary drive for color vision? It is striking how colorful the man made environment is compared to natural settings. What was the selective pressure that made individuals with color vision survivors-breeders in our natural habitat? (288)
This is a fascinating question that cannot be answered easily or succinctly. It is a fun topic to ponder over an ale or two at pub. Much has been written on the topic and I would suggest that it is worthwhile and fascinating to review some of the literature. A brief introduction is given by Gouras on this website. Also Chapter 6, "The ecology and evolution of primate color vision," in "Color Vision: From Genes to Perception" by Gegenfurtner and Sharpe is a nice summary.

It is generally accepted that the short-wavelength sensitive cones evolved first as a distinction from a single cone type sensitive to longer wavelengths. The evolutionary advantage of this might have been a better capability to sense changes in the illumination (and also to discount the effects of such changes when searching for objects). Knowing about changes in illumination helps one to better respond to changes in weather and time of day. Perhaps it helped those early primates with simple color vision to be on time for dates with primates of the opposite sex and therefore fair better in the selective breeding process? The ability to perceive red-green differences evolved later and that is often attributed to improving the ability to find good (as in ripe) food more quickly. Ripe food tends to vary from it's surrounding vegetation in a red-green direction in color space. It might also be useful in judging which prospective mates are available and interested in mating.

I don't think the idea of improved spatial resolution is consistent with the evolution of color vision. The best spatial resolution would be obtained by having a single cone type with a relatively narrow spectral response. This would minimize the effects of chromatic aberration and maximize the spatial sampling of the cones. Of course there are tradeoffs between color vision, spatial resolution, and overall sensitivity that must be made during the evolutionary process. Plenty to ponder when considering how we ended up with the very efficient and functional visual system we have. (Back to top)


When is white not white? (283)
"Mu!" (Back to top)


How does the yellowing of the lens with age affect: colour vision, scotopic vision and the contrast of tests charts that are spectrally neutral? (281)
In general as the lens ages it becomes more yellow and also scatters more light. It also hardens such that we can no longer accommodate to near viewing distances and have to wear reading glasses. The yellowing is caused by absorption and scattering. To answer your questions. (a) Color vision is not affected as much as we might think because our visual systems adapt to the yellowing and the world still appears fairly normal (it doesn't take on a yellow cast). However, certain colors will be influenced more than others. Blues will look darker and purple colors will look more like reds. The main effect is that colors that matched when we were young might no longer match as we age. This is just like what happens if we put on yellow sun glasses and looked at various color matches. (b) For scotopic vision, there is less light that the rods are sensitive to in the blue region of the spectrum. This results in a decrease in scotopic sensitivity. In other words, it gets harder to see at night. The shift in spectral sensitivity for scotopic vision is probably not important perceptually. The increased scattering also makes it harder to see at night when light sources (like oncoming headlights) are present. (c) The perceived contrast of all stimuli goes down due to the increased scattering. Since much of this scattering is in the blue region of the spectrum, some of the perceived luminance contrast can be recovered by wearing yellow lenses that remove the blue light before it can be scattered in the eye. (Back to top)


I measure animal colouration, in particular contrast, which is dependent on spot size, not just area coverage. I cannot measure the spots on a lizard belly, but I can get a numerical matrix from a digital photo. Can you help me calculate perceived contrast? (274)
Given your point about equal areas of black and white producing different contrast depending on the spot size, you will not be able to do simple statistics on just the colors and area of colors. Instead you need to also factor in the size of the patterns. In image processing and visual perception, we would say that you need to analyze the spatial frequency of the pattern and compare that to the human contrast sensitivity function (CSF) to see which patters we are more, or less, sensitive to. This can get quite complex and requires assumptions about the viewing distance. That would be one approach, but I suspect it would make your analysis more complicated than it needs to be. Perhaps you can simply look at the average colors of the background and features (dots) in the photos (either in RGB, or LAB if you want something a little more perceptually meaningful), the relative areas of each, and the number of features (dots). That would give you five pieces of data you could analyze statistically (although area of background and area of feature might really be the same data if there are no other colors on that area of the animal). I would suspect that would give you something to correlate with your perception of contrast. (Back to top)


Can visual color discrimination be taught? Does color discrimination become better through practice? What affect does the aging of a person's eyes have on color discrimination? (272)
You can't really teach someone to improve their color discrimination. However, in some applications you can teach observers how to better look for the differences. For example in image reproduction, some observers typically overlook huge color differences that are clearly perceptible once they are pointed out. When observers are trained to look in the "right places" it seems like they have improved their color discrimination. They really haven't, they've just improved their observing skills. Also an observer's motivation can have an effect on their apparent ability to discriminate colors.

As people age, their ability to discriminate small changes in color often deteriorates to a degree. More importantly their color vision changes due to yellowing of the lens of the eye. This can result in metameric color matches for one observer being significantly different from those for another. Of course this is just as true for multiple observers of the same age as it is for a single observer as they age. (Back to top)


Why do painted walls of saturated complementary colors cause eyestrain when placed close to one another? (261)
It would depend upon the specific complementary-color combinations, but the most likely cause is accommodation changes due to chromatic aberration in your eye. Essentially, different colors are focused at different positions within your eye and your visual system must adjust its focus to view those different colors in optimal sharpness. If you are quickly looking back and forth between two very saturated colors, you are forcing your eyes to change accommodation (focus) rapidly just as if you looked back and forth quickly between near and distant objects. This is tiring and strains your eyes. Another contributor might be changes in chromatic adaptation since your eyes are trying to adapt to the two strong colors in succession. This effect is similar to sitting in a room and flipping the lights on and off repeatedly. That would also strain your eyes. (Back to top)


Do you have any training materials to illustrate color that I could use as an educational tool? (254)
We don't have any specific educational materials that we provide. Also you might be confusing us with the Munsell Color Company, part of GretagMacbeth. That's probably where you have color chips from. They don't provide educational materials, but there is a lot of information on their website. If you are looking for materials on the Munsell system, there are student sets available from Fairchild Books called "The New Munsell Student Color Set, 2nd Ed.". (Just as our lab is not related to the Munsell Company, Fairchild Books has no relationship to me!). A good general reference on color science and measurement is Roy Berns' Principles of Color Technology, 3rd Ed.. Lastly, if you are looking for educational materials that allow you to provide interesting demonstrations of various, I have had good luck with the material available from Arbor Scientific. (Back to top)


How should a color lab be designed? What colors should the walls and furniture be, so as not to influence the perception of color? (235)
There probably is no single correct answer to this question, but the general best practice is to have the walls and furniture a neutral gray to minimize the impact on the color judgements. A preferred wall paint would be similar to the gray inside a standard light booth. This is typically a neutral with a CIELAB L* of approximately 70. To avoid having a completely gray lab, it is sometimes pleasing to have some texture in the countertops or tabletops (like a granite texture) and black furniture can also be used. You also need to make sure you are using appropriate illumination for your application. Sometimes it is also helpful to paint the wall behind an observer black to minimize any reflection of ambient light from behind the observer onto the color stimuli being evaluated. Lastly, rooms were color measurements are made are often painted completely black to minimize any stray light bouncing around the room and contaminating the measurements. (Back to top)


My two eyes see color differently. What causes this? (233)
You have posed a very interesting question. Fortunately it has a rather simple explanation. There is an area on your retina called the fovea where you have the greatest concentration of cone photoreceptors and therefore the best visual acuity and color vision. When you look at an object, you move your head and eyes such that the image of that object falls on the fovea. The fovea is protected by a yellow filter called the macula. This yellow filter protects this important part of your retina from accidental high-intensity exposure to short-wavelength light (blue and ultraviolet light is partially absorbed by the yellow filter). It is very common for the density of this yellow filter to vary from person to person causing significant differences in color vision. While we don't normally notice a yellow tint to the world around us due to chromatic adaptation (our ability to adjust to overall changes in the color of the illumination), there are more subtle differences in vision that can be observed. It is also not uncommon for people to have differing amounts of macular pigmentation between the two eyes. An eye with greater density of macular pigment than will see colors slightly warmer (redder). This is nothing to be concerned about and usually goes unnoticed. You could probably find a light yellow filter that would equalize the perceptions and give you a rough idea of the differences between your two eyes.

Also, the lens in our eyes yellows as we age, providing another cause of differences in color vision between observers. However, it is not widely recognized that the lens yellowing would be significantly different from one eye to the other (although theoretically it could be and would be if, for example, an observer had cataract surgery on one eye). Refer to a book on visual perception for more details on the various eye structures mentioned above. (Back to top)


What are color vision deficiencies? How common are they? (231)
Color vision deficiencies result from either a lack of one or more cone types, or cones that behave somewhat differently from average. Those lacking long wavelength cone pigment suffer from protanopia. A related condition is anomalous protanopia, or protanomaly. Here, long wavelength cones are present, but their sensitivity is shifted spectrally to shorter wavelengths, so they interpret certain stimuli differently than normal observers. Similarly, deuteranopia (deuteranomaly) is the lack (spectral shift to longer wavelengths) of the middle wavelength cone pigment, and tritanopia is the lack of short wavelength cones (tritanomaly is incomplete tritanopis). It is important to remember than none of these conditions should be referred to as true color blindness. This is not simply a politically correct statement. In fact, those suffering from any of these conditions do experience color, but not in the sense that a color "normal" observer does.

Other less-common deficiencies are rod monochromacy and cone monochromacy. With rod monochromacy, there are no cones present, only rods. Persons suffering from this are truly color blind. With cone monochromacy, a person has only one cone type. For more details on these and other vision deficiencies, see reference 3.

From reference 2, percentages of the more common deficiencies:
Type Male %Female %
Protanopia 1.00.02
Deuteranopia 1.10.01
Tritanopia 0.0020.001
Cone monochromatism ~0~0
Rod monochromatism 0.0030.002
Protanomaly 1.00.02
Deuteranomaly 4.90.38
Tritanomaly ~0~0
Totals 8.00.4
(Back to top)


What is color? (230)
Color is that characteristic of a visible object or light source by which an observer may distinguish differences between two structure-free fields of the same size and shape, such as may be caused by differences in the spectral composition of the light concerned in the observation.[ref 1, p 723] In other words, color is that perception by which we can tell two objects apart, when they have otherwise similar attributes of shape, size, texture, etc.

OK, that's the textbook answer. This is admittedly unsatisfying, because color is an inherently subjective experience. Color only exists in our minds, and putting a scientific definition together of no easy task. The usual definition, given above, is really a circular argument. It amounts to: "Color is that attribute of an object leftover when you eliminate all attributes except color." So, if an two objects look different, but have the same size, shape, texture, etc., then the way you are telling them apart is their color. Still not satisfied? Here's another answer for you. (Back to top)


How do we see in color? (229)
In the retina of our eye are photoreceptors that are sensitive to light. When light is absorbed by the photoreceptors, the light energy is converted into electrical and chemical signals that the neurons in our eye and brain process. There are two kinds of photoreceptors in the retina: rods and cones. Rods mediate vision at lower levels of illumination. Cones mediate vision at higher levels of illumination. There are three types of cones with each type differentially sensitive to a different region of the visible spectrum. They are known as the Short-wavelength sensitive cones, the Middle-wavelength sensitive cones and the Long-wavelength sensitive cones. Sometimes they are referred to as R-, G-, and B-cones but these are misnomers based on the colors in the spectrum. For example, very short wavelength light can uniquely stimulate the S-cones but the sensation associated with this light stimulation has a reddish and bluish component. Fundamentally our color vision derives from comparisons between the amount of light being absorbed by each cone type. Our visual system compares the outputs of the cone types to process color. In addition, color appearance is influenced by the ratios of cone excitations in surrounding regions and by the overall levels of cone excitation caused by the prevailing illumination. These comparisons occur at different stages of processing that start in the retina and continue to the cerebral cortex of the brain. (Back to top)


What do we know about research done on colors & their meanings? (227)
This is indeed a very interesting question and one that comes up often. It is certainly true that color alone can evoke strong emotional and cognitive responses. However, the systematic study of such responses is somewhat uncharted territory. This is largely because many (if not all) of these responses are learned and we all have different life experiences. A color that evokes a very negative response, or meaning, to me could evoke great joy in another observer. There are also almost certainly cultural differences in the meaning and interpretation of colors. That said, some research is done on the topic. One place to learn about it is in the journal "Color Research and Application". Another place you might look for some introductory information is the Color Association of the United States Color Association of the United States. A good overview reference on the topic is chapter 5 of the first edition "The Science of Color" published by the Optical Society of America. The title of the chapter is "Psychological Concepts: Perceptual and Affective Aspects of Color". Unfortunately that topic is not covered in the second edition of the book. Another interesting book with some prototypical psychological interpretations of various hues is "Color Bytes: Blending the Art and Science of Color" by Bourges. (Back to top)


What does it mean to be color normal? (226)
A color normal individual is one whose color vision is not greatly different from the average person. This may seem obvious, but remember that the color vision deficiencies are, in most cases, not simply on/off conditions. There is a continuum of, for example, deuteranomalous people. Some will have only a slight shift in middle-wavelength cone sensitivity and others may have so large a shift that middle-wavelength cone behavior is no longer distinguishable from that of long-wavelength cones. A series of color-matching experiments can determine what type of deficiency a person might have. The end result is usually simply an understanding of approximately how far from average an individual might be. To state a cutoff between normal and anomalous vision assumes some criterion which is application specific. In other words, just how normal you are depends on just how normal you need to be for your task. If you are a taxi driver, you certainly need to determine the color a traffic signal. If you are an interior designer, you probably need somewhat better color vision to please your customers. (Back to top)


What parts of the eye are important for color vision? (225)
Click on the image for a larger view
Use by permission from reference 4.

 Most of the important parts of the eye are labeled on the diagram. The cornea and lens focus the image onto the retina. The retina is the part that actually detects incoming light. The iris adjusts in width to partially account for light levels. The fovea is the central focal point of the eye. (That is, when we look at something, we are casting its image onto the fovea.) The fovea is the are where we get most of the spatial detail and color in what we see. The optic nerve is a bundle of nerves which carries the visual information to the brain. Not shown is the macula, which is a filter over the fovea. It serves to limit the damage that might be cause to the fovea if we accidentally focus on intense light sources, such as the sun.
(Back to top)


How do we select names for colors? (224)
This question has been of interest not only to scientists who study color and the visual system but also to linguists and philosophers. The conventional wisdom used to be that culture and language determined our use of color names. This view began to change in 1969 when Berlin and Kay published a book that showed that there is a high degree of universality in the use of color terms across cultures and languages. Now many investigators believe that there is a physiological basis for the use of certain basic color terms and the parsing of color space into categorical regions denoted by these basic color terms (black, white, gray, red, green, blue, yellow, purple, orange, brown and pink). There is evidence from animal studies and studies with infants to support this categorical view of color.

However, people do use many more color words; hundreds of different terms have been catalogued. It seems however that the non-basic terms are used without the same generality and consistency as the basic terms. For example, cyan may have a specific meaning to a couple of printers working together in a print shop but the man on the street may have an altogether different notion of what cyan is. Yet everyone, within the limits of the homogeneity of normal color vision, will agree about the meaning of orange or pink. (Back to top)


How are cones organized in our eyes? (223)
During the development of the embryo, part of the neural tube which develops into the central nervous system forms outcroppings that extend and develop into the retinas. Therefore the retina is considered part of the brain: a part that is easily accessible for study. The retina consists of 5 layers of cells and between each layer there are extensive interconnections in which visual processing takes place. There are about 125 times as many receptors in the retina as there are ganglion cells in the optic nerve, which connects the eye to the brain. This gives an indication of some of the processing that must go on. Because the retina is so accessible, much is know about the processing of color. The signals from different cone types are segregated in opponent pairs during this processing so that ganglion cells have specific receptive fields that are excited by one cone type in the center and inhibited by another in the surround. Although the effects this organization can be evidenced in psychophysical experiments that measure different aspects of visual function, our conscious experience of color does not relate well to this organization. It is at the later stages of processing in the brain in which our subjective experience of color is processed. (Back to top)


What spatial and temporal processing takes place in the eye? the brain? (222)
Subjectively, we experience many different qualitative aspects of vision, for example, form, color, motion, depth, etc. This information is all input into the visual system through the photoreceptors in the retina. Therefore the retina has to process the information to preserve all these different aspects of the visual stimulus. The term multiplexing is often used to describe the way the early visual system simultaneously sends this varied information to the brain. Specialized pathways are determined very early in visual processing. The second layer of retinal cells already has specialized neurons that process form by creating center-surround receptive fields. Different types of temporal response are seen in cells with either sustained or transient responses in the next layer of processing. Two streams of visual processing have been identified at the optic nerve level. One responsible for fine detail and color and the other responsible for detecting rapid temporal change with high sensitivity to changes in contrast. (In other animals, cells that respond to directional motion are already present in the retina.)

In the brain we see evidence of hierarchical and modular processing of visual information. At the early stages of cortical processing, cells exist that respond to stationary or moving edges and bars of light contrast, evidence of form processing. At later stages of cortical processing we find areas of the brain that seem to be specialized for the processing of specific visual attributes. For example area MT in the temporal lobe shows a specialization for motion detection. Not only do cells here respond best to moving stimuli with specific characteristics (direction and speed) but also studies with animals has demonstrated that artificially stimulating these cells can influence the perceptual judgments of motion. In monkeys, an area called V4 has been identified as being critical for the processing of color. It has been shown that humans with brain damage in the area homologous to this one lose color vision. (Back to top)


What is chromatic adaptation? (221)
Chromatic adaptation is the ability of the human visual system to adjust itself in response to varying illuminant conditions. In other words, we adapt to the color of the light source in order to better preserve the color of objects. For example, if viewed under incandescent light, white paper has a decidedly yellow cast. However, we have the ability to automatically account for the yellowish light, and we therefore see the paper as white. If you think about it, this makes a lot of sense. It would be a very confusing world if objects were changing color every time the light source changed. From an evolutionary point of view, we still need to know if the fruit is ripe whether it is morning, noon, or evening. Chromatic adaptation makes this possible. (Back to top)


How do we characterize a person’s color vision? (220)
There are several test available, depending on what aspects of color vision you wish to focus on. The Farnsworth-Munsell 100 Hue Test presents the observer with 80 color disks and a few anchor points. The observer must order the disks between each anchor point. The color span the whole circle of hue space, and mistakes made are plotted on a polar graph, the angle corresponding to hue, and the distance from center increasing with error in disk placement. General trends, such as large errors in the red/orange region, can be mapped to specific vision deficiencies. Observers with poor performance throughout the hue circle are not necessarily color deficient, but they do lack good color discrimination.

Another popular test are psuedoisochromatic plates. The most common of these are Ishihara\'s Tests for Color-Blindness. These plates, common in grade school vision testing in the U.S., consist of dots of various colors. Plates contain a number or letter which is only visible to observers with the ability to distinguish between the various colors of the dots. This test is not designed to accurately predict specific vision deficiencies, but rather as a general screen for color vision defects. (Back to top)


How many colors can we see? (219)
This is a very popular question and it is usually answered vaguely by, "Millions and millions!" However, it is better to ask the question in a more specific way to get a more comprehensive answer.

Many of us can select a setting for our computer monitors that displays millions of colors and we see an improvement in image quality with this setting. However, if you select the colors correctly you can reduce the number of colors to a couple of hundred or even fewer (depending on the image) without noticing a degradation in quality. This would indicate that we can’t see millions of color variations simultaneously.

One way to answer the question is to measure the ability of people to discriminate colors. Many researchers have investigated chromatic discrimination by varying the wavelength of two monochromatic lights until they are just noticeably different. Other studies have used the variability of color matching to gauge discriminability and yet others have directly measured threshold differences throughout color space. Using these measures we find that our visual systems can discriminate millions of colors.

In our laboratory we are interested also in larger than threshold color differences: the type of differences that would make you reject a certain touch-up paint because it’s not a close enough match to the color of the paint of your car. Even with such a metric there are close to a million discriminable colors on a computer monitor which only can reproduce a fraction of the colors we can see out in the real world. (Back to top)


References

  1. G. Wyszecki and W.S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae 2nd Ed., Wiley, New York, 1982.
  2. R.W.G. Hunt, Measuring Colour 3rd Ed., Fountain Press, England, 1998.
  3. R.M. Boynton, Human Color Vision, Special Limited Edition, Optical Society of America, Washington D.C., 1992.
  4. M.D. Fairchild, Color Appearance Models Addison-Wesley, Reading, Massachusetts, 1998.
  5. R.S. Berns, Billmeyer and Saltzmann's Principles of Color Technology, Wiley, New York, NY, 2000. (from Wiley)
  6. H.G. Völz, Industrial Color Testing 2nd Ed., Wiley-VCH, Weinheim Germany, 2001.
  7. There are several links to GretagMacbeth's Color Conversion Freeware