Patent ID: 8600283

Claim:
An image forming apparatus comprising: plural image forming units of corresponding plural colors, each of the image forming units including, a print head including plural LED chips aligned in a main scanning direction, each of the LED chips including plural LEDs aligned in the main scanning direction, and a photosensitive body on which light from the print head is received; a displacement amount obtaining unit that obtains, for each of the colors, an amount of displacement of each of the LED chips of the print head in a sub-scanning direction with respect to a reference position; a mark forming unit that forms, for each of the colors, an alignment mark for detecting an amount of skew of the print head with respect to an axis direction of the corresponding photosensitive body while correcting the amount of displacement of the LED chips of the print head; a skew detection unit that detects, for each of the colors, the amount of skew of the print head; a screen angle selecting unit that selects screen angles for the plural colors respectively based on the amounts of skew of the plural image forming units detected by the skew detection unit; an image processing unit that performs image processing on input data to be expressed by pixels of the plural colors such that the pixels of each of the colors have the screen angle selected by the screen angle selecting unit; a correction amount determining unit that determines a total amount of skew correction based on the amount of skew detected by the skew detection unit, and determines the amount of skew correction in the sub-scanning direction for each of predetermined groups of the pixels for shifting the pixels of the image data corresponding to the group in the sub-scanning direction, based on the total amount of skew correction, for each of the colors; and an image forming control unit that controls forming an image by the plural image forming units based on the image data processed by the image processing unit while correcting the amounts of displacement of the LED chips of the print heads and the skew of the print heads.