Image reading apparatus for correct positioning of color component values of each picture element

An image reading apparatus in which a set of image sensors for outputting color component values of each of a plurality of picture elements by reading out image data from an original image are arranged in parallel to a main scanning direction and at separate positions in a sub-scanning direction, said color component values including a first color value, a second color value and a third color value, said image reading apparatus comprising:

• a reference pattern having slanting lines described in black on a white background, said reference pattern provided outside a reading range and read by the image sensors prior to the original image;
• reference-position determining means for detecting one of the slanting lines in the reference pattern based on image data having the third color value output by one of the image sensors so that a position of the image data when said one of the slanting lines is detected is determined as a reference position;
• first delay means having a plurality of first line memories for storing image data having the first color value read out from the original image having a plurality of lines, said first delay means delaying outputting of the image data from the first line memories line by line;
• first determining means for determining image data having the first color value at first imaginary points based on the image data from the first delay means;
• second delay means having a plurality of second line memories for storing image data having the second color value read out from the original image having the plurality of lines, said second delay means delaying outputting of the image data from the second line memories line by line;
• second determining means for determining image data having the second color value at second imaginary points based on the image data from the second delay means;
• error measurement means for selecting one of the first imaginary points whose image data has a minimum difference between the first color value and the third color value of the image data at the reference position based on the image data determined by the first determining means so that a first error is determined by the selected one of the first imaginary points, and for selecting one of the second imaginary points whose image data has a minimum difference between the second color value and the third color value of the image data at the reference position based on the image data determined by the second determining means so that a second error is determined by the selected one of the second imaginary points;
• first line correcting means for outputting image data having the first color value of each picture element at a corrected position based on the image data from the first delay means by using a predetermined interpolation function, the interpolation function having a set of correction factors determined based on a distance between the first error and the reference position;
• and
• second line correcting means for outputting image data having the second color value of each picture element at a corrected position based on the image data from the second delay means by using the interpolation function, the interpolation function having a set of correction factors determined based on a distance between the second error and the reference position.