Ames and his students. Photomosaic: Courtesy of William Ames

For the past 12 years, William Ames, a senior lecturer in computer science, has posted two pictures of himself on his Boston College webpage. One is a headshot taken by a University photographer, the other is a computer-generated photomosaic of the same image, assembled from more than a thousand photographs of his current and past students.

Ames designed computer processors and software in the private sector (at Hewlett Packard and Silicon Compilers) before joining Boston College in 1995 to teach courses in computer graphics, web application development, and digital signal processing, among other topics. He wrote the photomosaic program in 2000 with his teaching assistant Matthew McLaughlin ’00 (now vice president of technology at a Social Security advocacy firm), using University I.D. photographs contributed by his students.

To create the mosaic, the program reads the shade of gray of each pixel in each student photo as a number between 0 (black) and 255 (white). It then rapidly swaps out the photographs until the numeric differences between each student photo and each fragment of the professor’s image are minimized. For example, to match Ames’s bone-white collar button, an average shade of 220, the program cycles through student photographs until it selects one with a high preponderance of pixel numbers near 220. When viewed on a screen, the beginning of the sorting process looks like TV “noise”; gradually, a pointillist image emerges in black, white, and gray. Ames has tried using color photos, he says, but, among other difficulties, he finds that too many students sport Boston College attire, tipping the end product into the red part of the spectrum. In 2000, it took Ames half an hour to complete a black-and-white mosaic. Today, with speedier computer processing, the program performs over 44 million swaps and finishes in less than three minutes. The image above is the fifth iteration Ames has produced. It contains the 1,364 most compatible student photographs from a collection of 1,619. Ames notes that other photomosaic software programs create smoother composite images, by altering the component pictures. “I didn’t do any of that,” he said. “I left all of the individual pictures and their pixels as is. I wanted this as a way of remembering my students.”

—Zak Jason

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