Patent ID: 8467102

Claim:
An 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 screen processing unit configured to perform a screen process for dot image data to obtain a quantized image data based on a dither matrix, where a position of a dither matrix element is shifted in accordance with both a shift amount of a scan line in a sub-scanning direction on an image carrier of the image forming unit and a rotational angle of a rotation process to be applied to the quantized image data; a rotation processing unit configured to rotate the quantized image data by the rotational angle; a registration error correction unit configured to shift, in the sub-scanning direction, a position of each pixel of the quantized image data obtained by said screen processing unit, so as to offset the shift amount of the scan line in the sub-scanning direction on the image carrier of the image forming unit; and an interpolation processing unit configured to adjust pixel values of pixels of the quantized image data generated by the screen process using the shifted dither matrix, between preceding and succeeding pixels in the sub-scanning direction, so as to smooth a step generated due to the shift of the position of each pixel by the registration error correction unit.