an intermediate-data generating unit that generates intermediate data including information about a rendering object on a page based on the input rendering command;

an RGB bitmap generating unit that generates an RGB bitmap image of the page based on the intermediate data obtained in the intermediate-data generating unit;

an attribute-bitmap generating unit that generates an attribute bitmap image including attribute information corresponding to each pixel forming the RGB bitmap image based on the intermediate data obtained in the intermediate-data generating unit, wherein the attribute bit map image indicates whether printing of each pixel should be performed with only K or with MCYK;

a determination unit that performs a color/monochrome determination for each pixel of the RGB bitmap image based on both the attribute bitmap image obtained in the attribute-bitmap generating unit and the RGB bitmap image obtained in the first-bitmap generating unit, the determination unit determining that a pixel is monochrome only when the RGB bitmap image thereof indicates R=G=B and the attribute bit map image indicates that printing of the pixel should be performed with only K; and

a conversion unit that converts the RGB bitmap image obtained in the first-bitmap generating unit to the MCYK bitmap image based on a determination result obtained in the determination unit, MCY of a pixel of the MCYK bitmap image being 0 when the determination result for the pixel is monochrome.