Patent ID: 7982908

Claim:
A color image forming apparatus for forming a color image on a recording medium by using a plurality of coloring materials including at least a black coloring material and having a density sensing unit for detecting a density of an unfixed test image, comprising: a test image forming unit configured to form one time, on a recording medium, both a plurality of first test images, each having different tonality of the black coloring material, and a plurality of second test images of a mixture of cyan, magenta and yellow coloring materials, each having a reference tonality, each second test image corresponding to one of the plurality of first test images, and to fix both the first test images and the second test images on the recording medium; a color sensing unit configured to detect, respectively, color values of the first test images and the second test images, which are formed one time and fixed on the recording medium by the test image forming unit, wherein the color values of the first test images comprise lightness values and hue values; a first acquisition unit configured to acquire tonality data of black corresponding to a tonality of each of the first test images based on the lightness values of the color values of the first test images detected by the color sensing unit, wherein the tonality data of black acquired by the first acquisition unit corresponds to a target lightness based on an estimated lightness line defined by the tonality data of the black coloring material used for the first test images and the lightness values of the color values of the first test images detected by the color sensing unit; a second acquisition unit configured to acquire target hue values based on an estimated hue line defined by the tonality data of the black coloring material used for the first test images and the hue values of the color values of the first test images detected by the color sensing unit; and a calculation unit configured to set the target lightness and the target hue values as target color values, and to calculate tonality data of the cyan, magenta and yellow coloring materials on the basis of the target color values and the color values of the second test images detected by the color sensing unit, wherein the target color values are based on the same first test images which are formed one time by the test image forming unit.