Patent ID: 7342687

Claim:
A light source stability determination method applied to an image reading apparatus in which an imaging device formed by pixels arranged in one line detects light reflected on a white reflection surface having a uniform reflection ratio by the respective pixels, white correction values are calculated for the respective pixels based on amounts of the detected light, said imaging device detects light reflected on a manuscript by the respective pixels and generates first electric signals having signal levels corresponding to amounts of the detected light, and the signal levels of the first electric signals generated from the respective pixels are corrected by the correction values, said method comprising: irradiating light to said reflection surface from a light source constituted by a cold-cathode tube; detecting light reflected on said reflection surface by the respective pixels of said imaging device; determining whether or not a light amount obtained by the one line of pixels from said light source is within a predetermined range, based on light amounts detected by the respective elements; starting calculation of the correction values, generation of the first electric signals, and correction of the signal levels of the first electric signals with the use of the correction values, in a case where it is determined that the light amount obtained by the one line of pixels from said light source is within the predetermined range; generating second electric signals having signal levels corresponding to the light amounts reflected on the reflection surface and detected by the respective pixels; generating waveform data representing the signal levels of the second electric signals corresponding to the one line of pixels; determining whether or not there is a distortion in the waveform data corresponding to the one line of pixels; and determining that the light amount obtained by the one line of pixels from said light source is within the predetermined range, in a case where it is determined that there is no distortion in the waveform data.