Abstract: Data to be stored in a frame buffer (12) that stores data representing an image are drawn from a look-up table (34). The look-up table (34) contains conversion data and is addressed by the output of a multiplexer circuit (24). The multiplexer circuit (24) receives its inputs from the data output port of the frame buffer (12), from a register (42), and from an analog-to-digital converter (22) that converts the output of a video camera (20) to digital signals. In response to different values on selection-signal lines (36), the multiplexer circuit (24) assembles the address that it applies to the look-up table (34) from different combinations of the outputs of the frame buffer (12), the register (42), and the analog-to-digital-converter (22).