Gamma correction is among the things most often done wrong by graphics programming novices. It's almost as bad as missing scene-related color transforms and linear volume sliders in the average video game. The code example in the readme should definitely mention to adjust.Gamma(img, 1/2.2) before doing any color mixing and adjust.Gamma(img, 2.2) before saving back to file (for as long as bild does not implicitly handle this, anyway) and link to some recommended reading.