If the grids of a color conversion table are simply downsampled, the way ink is used (the manner of the changeover in the value of a CMYKlclm signal) differs from that color conversion table before downsampling, there is a shift in the starting point of dark ink at the point of changeover of continuous tone ink, and a decline in image quality ascribable to downsampling of the color conversion table tends to occur. Accordingly, an original LUT is read in, a parameter for selecting a grid to be downsampled is set, a table of evaluation values for selecting a grid to be downsampled is created, a grid capable of being downsampled is selected by referring to the evaluation-value table, and table data that does not contain this grid is copied.