Colorizing the Prokudin-Gorskii Photo Collection

Sergei Mikhaliovich Prokudin-Gorskii (1863-1944) was a Russian chemist, photographer, and visionary who took some of the very first successful color photographs. From 1907 to 1915 Prokudin-Gorskii travelled Russia, making an extensive photographic survey of the country. His method of photography was to take three exposures of every scene on glass plates, one each using a red filter, a blue filter, and a green filter. He could then project his pictures back through colored filters using a ''magic lantern'' to recreate the full color images.



Prokudin-Gorskii's glass plates have since been purchased by the Library of Congress and digitized. We no longer need a ''magic lantern'' to see the pictures in full color, but can instead merge the color channels digitally.

Aligning the Images

For this assignment, I wrote a program which can automatically align the three separate channels of Prokudin-Gorskii's pictures, producing a color image. This is accomplished through the use of an image pyramid: first the program aligns a very small version of the image, then aligns progressively larger versions until the original scale of the image is aligned. In this way, a large window of displacements can be efficiently searched. For sake of this program, an image is considered to be in good alignment when the sum of squared differences between the color channels is minimized.

For some pictures, my program fails to align the color channels. This can happen when one of the three channels is significantly different from the other two. In this case, the sum of squared differences of the channels may be extremely large even when the channels are properly aligned. As a result, my program will output a misaligned picture which has a better distance metric than the correct result, but makes less visual sense.