PURPOSE: To provide an image forming apparatus realizing the printing conditions respectively optimum to a line image and a natural image, obtaining improved image quality and achieving optimization to enhance the utilization efficiency of a memory means.

CONSTITUTION: The attribute data of a natural or line image among the color data from a host is stored in an attribute memory 4 and image data is stored in a data memory 3 on the basis of the attribute data. The content of the data memory 3 is subjected to rasterization processing on the basis of the content of the attribute memory 4 by a rasterizer 6 to perform permanent visible display by a printer engine 7. At this time, attribute data is received from the attribute memory 4 and the operation corresponding to the natural image/line image is performed in a dot unit and the natural image is printed in 200ppi while the line image is printed in 600 dpi.