several kinds of predetermined modes when one mode is selected from the predetermined modes one of a color display and a monochromatic display is selectively performed on a screen of one of a color monitor and a monochromatic monitor or a screen of one of moniters each having different standard the reference data corresponding to the selected mode are read from the memory and stored in the registers when the selected mode is changed reference data stored in requisite registers selected by newly selected mode are automatically rewritten by the reference data selected by the newly selected mode without exchanging programs of the cpu application_number US 13121387 A description referring now to the drawings fig1 is a block diagram showing a whole constitution of an image display system employing an embodiment of the image processing apparatus according to the present invention in fig1 an image processing apparatus 1 displays an image on a screen of a crt display unit 3 under a control of a cpu 2 in addition a vram 4 stores dot data and character codes for an image display further a character generator 5 is provided for displaying characters and the character generator 5 reads out character patterns designated by the character codes stored in the vram 4 furthermore a read only memory rom 7 pre stores the programs used for the cpu 2 next description will be given with respect to an essential portion of the image apparatus 1 in conjunction with fig2 a and 2b in fig2 a and 2b the clock symbols c1 and or c2 adjacent to a component indicate that the clock signals are inputs thereto in fig2 b 10 designates a rom for storing several.