To improve the compression rate of drawing images, and to make color processing high-speed and highly precise by adding a signal of whether it is a color pixel or a monochrome pixel to an image region signal which is to be added to each pixel for distinguishing a character/figure/image present on an image after image formation.

There are set a drawing plane generating means for drawing an inputted drawing command into a bit map image, a means for generating a new drawing plane by overlapping an image object of the drawing command inputted at the time of generating the drawing plane with the already generated drawing plane with the use of a logical operation process attached to the drawing command, and an information plane generating means for generating an information plane to be used for determining an attribute to each pixel of the whole image from the drawing command and its attribute.