Carl Salvaggio, professor in the Chester F. Carlson Center for Imaging Science, and two imaging science Ph.D. students, Katie Salvaggio (no relation) and David Nilosek, produced a three-dimensional reconstruction of Cowboys Stadium, home of the Dallas Cowboys. Salvaggio and his students, along with a dozen undergraduate photography students from the College of Imaging Arts and Sciences, tested out this image-processing technique at night to build a 3D model.
Salvaggio and his team knew they would face challenges because of the stadium's glass façade.
"The most important step in doing a three-dimensional reconstruction is to find a point in one image and find its matching point in another image," says Salvaggio. "The problem with glass is there are no features. You either see through it or you see a reflection. If you move, the reflected objects change their physical position."
Prior to heading to Arlington, Texas, for the March 23 event, the students did a test reconstruction of Student Innovation Hall, a curved glass structure on the RIT campus.
"We tried it both during the day and at night a week before the Big Shot. We shot images and processed the data and it failed miserably."
They had also planned to mount the cameras on light poles in the Cowboys Stadium parking lot, but the poles posed their own problems. Wind gusts would move the poles slightly and the artificial light pouring off the poles would backscatter into the cameras. The students ultimately shot the images off of tripods.
The imaging science team arrived early in Arlington and shot images for three solid days and processed the data. All were failed attempts because of the reflections, but one last attempt the night before the Big Shot worked. Shooting after sundown, there was only internal light coming from the stadium and no external light being reflected from surrounding objects. The features remained in the same positions and provided good matches between images.
A Big Shot photograph is made with light provided by volunteers who use flashlights or camera flash units to "paint" a particular area of the landmark while RIT photographers shoot an extended exposure. All other lights are turned off.
The evening of the Big Shot, the RIT photographers shot four exposures with more than 2,400 volunteers manned with flashlights around the stadium. In between each exposure, the imaging science and photography students slightly moved their tripods along the stadium's perimeter to end up with 48 different views.
"Everything just came together," says Salvaggio. "It was luck. If it weren't a Big Shot scenario, this would not have worked. The flashlights were great because the reflections were going up to the sky and not reflected directly to our cameras. That worked really nicely."
The data had to be color corrected before being processed because the algorithms, which rely on color to find matches, would pass over pixels of the same object if the colors did not match. Ryan Harriman, a biomedical photographic communications major, color corrected the images. Then using a Russian-produced commercialized software called Photoscan, Nilosek knit together the 48 images of the stadium to produce a three-dimensional model.
"It was great having the imaging science program do something special for this Big Shot," says Michael Peres, associate administrative chair in the School of Photographic Arts and Sciences and one of the Big Shot organizers. "The students were innovating and problem-solving right up until we started shooting the exposures. To my knowledge, no one has ever made a 3D rendering of a timed exposure, so it's pretty cool to be in that company."