PURPOSE: To attain print-out to the utmost even when ink runs short.

CONSTITUTION: A color conversion circuit 10 converts an RGB input picture into a CMY signal. An under color elimination black color generating circuit 12 eliminates an under color of the CMY signal and generates a black (K) signal. A masking circuit 14 masks an output of the circuit 12 in matching with a characteristic of a printer. A masking circuit 18 masks a CMY output of the circuit 10 to provide an output of a CMY signal. The output of the circuit 18 is used when black ink runs short. A color conversion circuit 20 generates a luminance signal from the RGB input and a luminance density conversion circuit 22 converts a luminance signal into a black/white multi-value density signal. The output of the circuit 22 is used when the CM or Y ink runs short. A CPU 24 changes over a selector 16 in response to the residual state of ink and the selector 16 selects any of outputs of the circuits 14, 18, 22.