Images of the Russian Empire

The goal of this project is to construct colored images out of the glass plate images of Prokudin-Gorskii. He was a photographer who captured many beautiful scenes in the Russian empire using red, green, and blue plates, hoping to some day combine them to create the first colored images.

Because the three glass plate images are taken separately, they are not perfectly aligned when placed on top of each other. Thus, I used the Sum of Squared Differences in my algorithm to evaluate possible displacements around the center ([-15, 15] pixels). Once I run SSD on the blue and green images, I align the green image with the given x and y offset, and then do the same with the blue and red images. At first, this worked well on 'cathedral.jpg' but not so well on 'monastery.jpg'. I realized that the black borders of the images were hurting my results and decided to crop out the edges of all my images. This produced great results and the SSD algorithm worked well on 'monastery.jpg' and 'tobolsk.jpg', and even improved 'cathedral.jpg'.

For much larger tif files however, SSD on a [-15, 15] pixel range is not enough to align an image. Increasing the range would be take too much to run, therefore I implemented the Gaussian pyramid algorithm for the larger images. I ran SSD on the smallest image (rescaled by a factor of 8), rescaled the image by a factor of 2 and aligned the image by the resulting offsets multiplied by 2. I ran this recursively until the image is at its original size. This algorithm allows for much less computation and incremental improvements at each level. The results were satisfying on the given images as well as a few that I picked from Prokudin-Gorskii's collection. There is still room for improvement, especially for 'emir.tif' due to different brightness values.