US Patent 7196725 Image reading apparatus and computer readable storage medium

In an X-ray film image reading apparatus, dark output distribution data of a CCD line sensor is corrected by using correction data. In order to suppress the influence of random noises on the correction data, a dark distribution correction data calculation circuit 10 calculates an average value or mode value of dark distribution outputs of all or some pixels of a CCD line sensor or a dark distribution output of the CCD line sensor subjected to a spatial low-pass filtering process, and stores it in a dark distribution memory as correction data. Next, a light source is turned on, and a subtractor subtracts the stored correction data from an output of the line sensor read from an X-ray film while the light source is turned on.