1. A computer-implemented image-wide matting process, comprising using a computer to perform the following process actions: generating main and secondary color layers, wherein the main color layer comprises a main pixel color value for each pixel location of the image which specifies a pixel color deemed to be a majority contributor to the pixel location, and wherein the secondary color layer comprises a secondary pixel color value for each pixel location of the image which specifies a pixel color deemed to be a minority contributor to the pixel location; generating an alpha layer, wherein the alpha layer comprises an alpha value for each pixel location of the image which specifies the portion of the pixel color of the location attributable to the color value of the main color layer for the pixel location; and generating a noise layer, wherein the noise layer comprises a noise value for each pixel location of the image which specifies the difference in color between a predicted pixel color defined by the majority contributor pixel color, minority contributor pixel color and proportion of the contribution of the majority contributor pixel color for the pixel location under consideration, and an observed color of that pixel location in the image.