Patent ID: 6911993

Claim:
An image forming apparatus for forming a color image by superposing component color images on the basis of arbitrary image information, the apparatus comprising: (a) an image transfer device; (b) a plurality of image forming units each for forming a plurality of mark images for a registration of component color images on the image transfer device; (c) a detector for detecting the positions of the mark images formed by the image forming units; and (d) a controller for controlling the image transfer device or image forming units on the basis of an output of the detector, wherein the controller obtains position data representing a forming position of each of the registration mark images with respect to a positional reference value arbitrarily determined to the registration mark images formed on the image transfer means, divides the position data of the mark images for each component color into each of a unit reference range representing a range in which one mark image is formed on the image transfer means, makes an operation processing for converting the position data divided for each unit reference range into a data in which each of leading edges of the unit reference ranges coincides with a leading edge of the positional reference value arbitrarily determined, extracts an overlapped position data representing the ranges common to mutually overlapping ranges of plural position data each of which is represented by a couple of position data corresponding to the rising and falling edges of a passage timing pulse subjected to the operation processing as read position data of the mark images for one component color, and calculates amounts of positional deviations of the component color images from one another on the basis of the position data extracted.