Patent ID: 8335026

Claim:
An image forming apparatus that reads an original and forms an image of the original that has been read, comprising: a skew amount calculation unit constructed to calculate a skew amount of the original for each position of a main scanning direction when the original has been read; an obtaining unit constructed to obtain from a storage unit a shift amount of a sub-scanning direction to an ideal scanning line of an optical beam used for image formation in the image forming apparatus, for each position of the main scanning direction; a color shift correction amount calculation unit constructed to calculate a color shift correction amount for correcting color shift in an output image by adding the skew amount calculated for each position of the main scanning direction and the shift amount obtained for each position of the main scanning direction; a color shift correction unit constructed to correct the color shift based on the calculated color shift correction amount; and a determination unit constructed to determine whether or not a pixel of interest coordinate in an image in which the color shift has been corrected is equal to or larger than a skew amount offset, wherein when the determination unit determines the pixel of interest coordinate is equal to or larger than the skew amount offset, data of the pixel of interest is output to an engine, wherein when the determination unit determines the pixel of interest coordinate is smaller than the skew amount offset, reading out of the pixel of interest is skipped, and wherein the skew amount offset indicates a drawing position in the main scanning direction based on the skew amount of the original.