Laboratory of Mathematical Science for Computing
Techniques for Restoring Faded Color Photographs
Since being introduced in the early 1900s, color photographs based on silver halides serve an important role in preserving historic information for future generations. However, many of these photographs are fading and deteriorating as they continue to age. The deterioration of a color film depends on factors including the storage environment and the age of the film, so it is generally not sufficient to simply apply a uniform, automatic procedure to recover the original image. Additionally, it was not clear if true restoration is even possible. Our laboratory was approached by iword, a Sapporo-based company interested in resolving this problem, to jointly develop techniques and software for restoring faded color photographs.
Many faded photographs contain an area where we can guess the original color, such as the sky, clouds or grass. We can begin by restoring these areas to their original color. However, there are infinitely many models that accomplish this restoration, and we wish to choose a simple model that effectively restores the image. In our joint research, we were fortunate to obtain for several images both the faded color film and prints that had been made before the image had heavily faded. By analyzing these images, we were able to determine that affine transformations can effectively map the faded colors (as vectors of primary colors) to their restored colors. This method requires four points where the original and faded colors are known, in order to completely restore the original image.
The attached image shows an image obtained from 60-year old original, faded film on the left, and the restored version produced with our techniques on the right. (The original faded film is provided by Ancient Orient Museum, Tokyo.)