I try to create an illumination invariant image with openCV like in this paper here: http://www.cvc.uab.es/adas/publications/alvarez_2008.pdf
Has someone an idea how one
+1 for the link to an interesting paper.
I guess I would build a function to convert to log, divide the channels, rotate by theta, and project onto one axis. Then I would build a function to measure the quality of the resulting invariant image. Then I would set up a search over theta to optimize the quality. That looks like what Alvarez is doing.
But first, I would study the Luv color space, it might be the closest approximation to this scheme that is possible without the special narrowband camera. Project the uv space onto a vector at angle theta, and see what happens.