Patent ID: 7616359

Claim:
An image reading apparatus for reading a color document as a monochrome image, comprising: a composite light source that irradiates the color document and includes plural light sources different in spectral distribution; a sensor configured to detect an intensity of a reflected light from the color document; a light emission ratio setting unit configured to changeably set light emission ratios different for the respective light sources; and a light source control unit to control effective light amounts of the plural light sources with the set light emission ratios, wherein, the light emission ratio setting unit includes a storage unit, the light emission ratio setting unit sets standard light emission ratios stored in the storage unit into the light source control unit the standard light emission ratios are calculated such that a product of a composite spectral distribution obtained by combining spectral distributions of the plural light sources with specified light emission ratios, spectral distributions of standard color charts, and a spectral distribution of a sensitivity of the sensor is integrated with respect to wavelengths to obtain first lightnesses for the standard color charts, a product of a spectral distribution of a standard light source, the spectral distributions of the standard color charts, and a spectral distribution of a visibility characteristic is integrated with respect to wavelengths to obtain second lightnesses for the standard color charts, and a square sum of errors between the first lightnesses and the second lightnesses with respect to the plural standard color charts different in color becomes a minimum.