US Patent 7133154 Image forming apparatus and masking coefficient calculation method

An image forming apparatus for calculating a masking coefficient is provides, in which the masking coefficient is calculated by using RGB input image signals obtained by reading a document of which spectral characteristics are known by an image reading part and CMYK output image signals optimal for reproducing a color of the document. The masking coefficient can be also calculated by using difference values between CMYK output image signals obtained from actually read RGB signals and optimal CMYK output image signals.