PURPOSE: To curtail the capacity of a memory, and to execute a high speed image processing by discriminating a specified color by a combination of an address signal which has been obtained in a data terminal and an address signal corresponding to the remaining video signal of video signals of three colors.

CONSTITUTION: Each density value G, B of green and blue is converted to digital signals GD, BD by analog-to-digital converters 14G, 14B, and inputted to a memory 16 as address signals. A digital signal BG from a data terminal D16 of the memory 16 and a digital signal RD from an analog-to-digital converter 14R are inputted to a memory 17 as address signals, respectively. In this way, by a combustion of these address signals, a binary data which has discriminated a specified color is outputted. In this way, the capacity of the memory can be curtailed, comparing with a conventional one.