Image reading apparatus, image forming apparatus and method

An image forming apparatus comprising:

• an optical system configured to scan a document surface in each of a main scanning direction and a sub-scanning direction orthogonal to the main scanning direction and generate a light image having size corresponding to a set reduction magnification;
• a monochrome CCD sensor provided along the main scanning direction and including a first photo-diode array configured to photoelectrically convert the light image;
• plural color CCD sensors each provided along the main scanning direction at a physical interval apart from the monochrome CCD sensor in the sub-scanning direction and including a second photodiode array configured to photoelectrically convert the light image;
• an AD converter configured to apply analog-to-digital conversion to each of analog outputs from the second photodiode array of each of the color CCD sensors and the first photodiode array of the monochrome CCD sensor;
• a delay processing unit configured to delay at least one of color image data of plural colors output by the AD converter and interpolate, with delayed any one or more of the color image data, a blank of image data that is to be read on a line in the sub-scanning direction;
• an inter-line correction unit configured to correct, at intervals and the reduction magnification, a positional deviation in the sub-scanning direction between the monochrome image data and the color image data of the plural colors, respective timings of which are aligned on the line by the delay processing unit;
• and
• an image forming unit configured to form an image having size corresponding to the reduction magnification according to an output from the inter-line correction unit.

An image reading method comprising:

• determining, according to a physical interval in a sub-scanning direction between a monochrome CCD sensor and each of plural color CCD sensors and a set reduction magnification, whether a line interval having an odd-number value is formed;
• executing normal reduction processing if a determination result is negative and generating, with the monochrome CCD sensor and the plural color CCD sensors, color image data of plural colors and monochrome image data from a document surface;
• and
• executing line delay if the determination result is affirmative, delaying at least one of the color image data of the plural colors, and interpolating, with delayed any one or more of the color image data, a blank of image data that is to be read on a line in the sub-scanning direction.