Photocopying

The general principle in color copying is the same as it is for black-and-white copying. The main difference is that the light reflected off the original document must be passed through three filters—one green, one blue, and one red—before it is transmitted to the photoconducting surface. Then, toner particles of three distinct colors—yellow, magenta, and cyan—must be available to correspond to each of the three document colors. The toners are added separately in three separate and sequential operations. These operations must be overlaid very carefully (kept "in register") so that the three images correspond with each other exactly to give a copy that faithfully corresponds to the original document.