Correction table forming method and image forming apparatus

Abstract

A main CPU reads out CMY values as γ correction patch data from an NVRAM, and outputs a γ correction patch from a color printer section via a γ correction patch output section. The output γ correction patch (sheet) is read by a color scanner sectionas RGB image data. The RGB image data is converted to CMY color signals by a color conversion sectionand input to the main CPU via a buffer memory. The main CPU calculates patch read data from the CMY color signals and compares it with the γ correction patch data stored in the NVRAM. The main CPU then calculates an inverse function of a curve of the patch read data and forms γ correction tables of four colors, C, M, Y and K. The γ correction tables are used for full-color γ correction. On the other hand, the main CPU performs an arithmetic operation (error correction) of an error correction table h(x), with an output of black (K) at screen angle −63° being f(x) and an output of mono-color black (K) at screen angle 90° being g(x). The error correction table h(x) is used for γ correction of mono-color black.