1. In apparatus for forming a composite image from at least first and second monochrome source images comprising first means for decomposing each of the source images into a set of a plurality of component patterns and deriving a monochrome composite image in response to a weighted average of amplitudes of the component patterns of the source images; the combination therewith of: second means for assigning amplitudes of a first of opponent colors to first component patterns of a source image in accordance with their normalized weight contribution to said weighted average of the amplitudes of the component patterns of the source images; and third means for assigning amplitudes of a second of said opponent colors to second component patterns of a source image in accordance with their normalized weight contributions to said weighted average of the amplitudes of the component patterns of the source images; and fourth means responsive to outputs from said first, second and third means for augmenting said monochrome composite image with said first and second opponent colors thereby to provide a color composite image.