Image processing using derived correction amount

Abstract

Color shifting correction is performed first based on shifting amount information indicating a shifting amount with respect to the scanning direction on an image carrier of each image forming unit, and halftone processing is then performed, thus suppressing caused by color shifting correction, and forming a high-quality image. An image forming engine has color shifting amount storage units storing actual shifting amounts with respect to ideal scan directions on image carriers in image forming units. Color shifting correction amount arithmetic units calculate color shifting correction amounts for respective color components using stored color shifting amounts. Color shifting correction units perform color shifting correction by converting coordinates upon reading image data from bitmap memories using calculated color shifting correction amounts, and perform tone correction. Data after tone correction undergo halftone processing. PWM processors generate PWM signals for scanning, and output them to exposure units of respective image forming units.