PURPOSE: To prepare hard copies simply, by preparing the result of multiplication of ink data resulting from complementary conversion and the masking coefficient as a table, and by providing an operational means to read out the product with reference of the table and an operational means to add a readout.

CONSTITUTION: With reference to γ-characteristic conversion tables 1W3 for γ-compensation of image data set according to the kinds of inks and printers, component conversion tables presetting me result of multiplication of ink data 4W6 resulting from complementary conversion of color image data and the masking coefficient, and the γ-characteristic conversion table of input image data γ-compensation is carried out: the product is read out by operational means 16W18 with reference to the component conversion table according to the ink data; the readout is added to achieve masking calculation; and the operational result is printed out by the printer. At this time, the γ-conversion tables is set according to the kinds of inks and printers in observation through the monitor.