1. An image processing apparatus comprising: an input unit that inputs a graphic drawing instruction based on image data; a drawing processing unit that obtains and holds a bitmap pattern corresponding to the specified concentration, based on the input graphic drawing instruction to fill an optionally specified range in a page memory using a specified concentration, calculates a coordinate position of holding the bitmap pattern corresponding to the specified coordinate position in the page memory, and writes the drawing data using the bitmap pattern of the corresponding specified concentration in a tiled pattern, into the specified range in the page memory, following the obtained coordinate position; and an output unit that outputs the drawing data written in the page memory, to an output apparatus, wherein the drawing processing unit decides whether the bitmap patterns to be used in adjacent specified drawing ranges are the same, links the specified drawing ranges to which the same bitmap pattern can be applied based on a result of the decision made, specifies again the drawing range in the page memory, and batch writes the bitmap pattern into the adjacent specified drawing ranges.