Patent ID: 8379279

Claim:
A color image forming apparatus which has, for each color component, an image forming unit for forming an image, and which forms a color image by compositing images of respective color components, the apparatus comprising: a scan line changing processing unit configured to shift a position of each pixel in a sub-scanning direction for each color component of dot image data to be processed, so as to offset a shift amount of a scan line in the sub-scanning direction on an image carrier of the image forming unit; a type determining unit configured to determine an image type for each color component of the image data to be processed; an interpolation determining unit configured to determine, based on the image type determined by the type determining unit for each color component, whether to perform an interpolation process to smooth a step of one pixel generated by shifting the dot image data by the scan line changing processing unit; and a changing unit configured to, when the image type is common to the respective color components and interpolation determination results are different between the respective color components, changing the interpolation determination results to make the interpolation determination results of all the color components coincide with each other, wherein the type determining unit includes pattern image determining unit for determining whether an image to be processed is a pattern image including a repetitive pattern, and a continuous tone image determining unit for determining whether the image to be processed is a continuous tone image having a continuous tone, wherein the interpolation determining unit determines not to perform the interpolation process when the type determining unit determines that the image data to be processed represents a continuous tone image, and to perform the interpolation process when the type determining unit determines that the image data to be processed does not represent a continuous tone image, and when the type determining unit determines that images of all the color components to be processed are pattern images, interpolation determination results obtained by the interpolation determining unit for all the color components do not coincide with each other, and a color component determined by the type determining unit to be a continuous tone image exists, the changing unit changes an interpolation determination result for the color component to an interpolation determination result of remaining color components.