1. A method, comprising: dividing a color digital image from an image sensor into a plurality of blocks; calculating a correlation (Cor) matrix of RGB channels of said image sensor; estimating a correlation matrix (Cor NN ) for an image sensor noise; calculating a color conversion matrix using Cor and Cor NN , as in C NEW =C NOMINAL (Cor−Cor NN ) T (Cor −1 ) T , where C NOMINAL is a second color conversion matrix calculated for the whole picture image; and applying said color conversion matrix C NEW to all pixels in a block, block by block.