Patent ID: 8218196

Claim:
An image processing method for color conversion from image data represented in an RGB color system and outputted from a reading device for reading a document, into image data represented in a YMC color system by using a color conversion table where a plurality of regions sectioned into blocks in a color space of RGB color system are associated respectively with predetermined tone values of Y (yellow), M (magenta) and C (cyan), the image processing method comprising the steps of: carrying out shading correction for, in a case where tone values of R (red), G (green) and B (blue) for representing white are larger than tone values of R, G and B for representing black, adjusting output values of the reading device which are obtained in reading a reference of white from the reading device, to a predetermined first reference value smaller than a maximum tone value, and adjusting output values of the reading device which are obtained in reading a reference of black from the reading device, to a predetermined second reference value larger than a minimum tone value, and in a case where tone values of R, G and B for representing black are larger than tone values of R, G and B for representing white, adjusting output values of the reading device which are obtained in reading the reference of white from the reading device, to the predetermined second reference value larger than the minimum tone value, and adjusting output values of the reading device which are obtained in reading the reference of black from the reading device, to the predetermined first reference value smaller than the maximum tone value; and carrying out color conversion by using a color conversion table obtained by expanding ranges around the predetermined first reference value and the second reference value in the color conversion table, ranges being included in the regions of RGB color system associated respectively with predetermined tone values of Y, M and C, in a case where at least any one of output values of R, G and B outputted from the reading device after reading a document is out of a range between the predetermined first reference value and the predetermined second reference value.