Nondiagonal color correction

A new color correction method is introduced which predicts how changing the color of the scene illuminant will affect a camera´s RGB response. Like diagonal transformation color correction methods, the new method requires only 3-parameters. It therefore requires only the RGB color of the two illuminants be known. The method models the 9-parameters of a 3-by-3 linear transformation using a 3-dimensional linear model composed of 3 basis transformations. Experiments show that the method works better than the standard diagonal model unless the camera sensors are very sharply peaked, in which case the performance is essentially unchanged.