Image reading apparatus, image reading method and program

An image reading method of an image reading apparatus that comprises a plurality of line sensors that are disposed in mutually different positions in a conveyance direction of an original document, and that respectively read the original document in line units and respectively output a read signal of a different color, the method comprising:

• in correlation detecting means, setting, as a reference signal, the read signal that is output from one of the plurality of line sensors, and detecting a correlation between the reference signal and each of a plurality of read signals output from other line sensors in a plurality of lines that are displaced in predetermined line units from a line from which the reference signal is read, such that positional displacement in a sub-scanning direction between the line sensors is corrected and, line positions of read signals of each color are aligned;
• and
• in selecting means, selecting a read signal having a high correlation with the reference signal as a read signal from the line of the reference signal, based on a result of the detection performed in the setting and detecting performed by the correlation detecting means,
• wherein the correlation detecting means comprises:
• in calculation means, calculating an absolute difference between the reference signal and the plurality of read signals output from the other line sensors, for each of a plurality of pixels included in each of the plurality of read signals;
• and
• in specifying means, specifying, for each pixel, a read signal having a high correlation with the reference signal based on the absolute differences calculated by the calculation means for the pixels included in each read signals, and
• the selecting means selects a read signal including a largest number of pixels that have been specified by the specifying means to have a high correlation as a read signal from the line of the reference signal.