Image reading apparatus and method of determining gain value and offset value for image reading apparatus

摘要

An image reading apparatus includes a light source for irradiating an original; a photoelectric converter for converting light reflected from the original to an analog signal; an A/D converter for converting the analog signal corresponding to each pixel from the photoelectric converter to the digital signal; and an adjusting device connected between the photoelectric converter and the A/D converter for performing an offset processing and a gain processing of the analog signal from the photoelectric converter. A memory stores a relational formula representing a correlation between an offset value for the offset processing and a gain value for the gain processing. An offset value calculating device obtains an offset value corresponding to a gain value used in the gain processing of the analog signal by using the gain value and the relational formula stored in the memory.