This is almost identical to a problem I'm trying to solve, which is to turn a potato-quality picture of a sheet of paper into a clean scan, turning whatever levels of gray conform the paper background become a uniform #ffffff white. The obvious solutions (equalizing, converting to bitmap, …) don't work because what's white in the top left (say #ccc) is wildly different from what's white in the bottom right (say #888), and the shift is non-uniform due to potato-quality lighting.
Glad I caught this post, I hope the solution can contribute to my problem (although I do not have a way to obtain a fixed ground truth — lighting will change for each picture.)
Glad I caught this post, I hope the solution can contribute to my problem (although I do not have a way to obtain a fixed ground truth — lighting will change for each picture.)