In a system for processing full-color image data, such as within a digital color printer or copier, a four-channel architecture is used. Three of the channels handle image data relating to primary color planes, such as CMY. In the other channel, values relating to the K value which goes with the CMY values for each pixel alternate with a B value, suitable for pure monochrome rendering of the pixel in the image. When it is desired to print or display the image in monochrome, the B values are isolated from the K values.