Patent ID: 8154762

Claim:
An image forming apparatus comprising: a conversion unit constructed to convert input color image data into color separation data, which is used for forming a color image on a printing medium using color materials respectively corresponding to cyan, magenta and yellow, which are basic colors, and a color material of a special color; and an image forming unit constructed to form a color image based upon the color separation data converted by the conversion unit; wherein the color separation data comprises a plurality of color data corresponding to each of the basic color materials of cyan, magenta, yellow, and the color material of the special color, wherein a hue of the special color is reproducible by combining a first color material and a second color material, which are selected from among basic colors neighboring the hue of the special color in a color wheel, wherein a brightness corresponding to a maximum saturation that is reproducible by the color material of the special color is higher than a brightness corresponding to a maximum saturation that is reproducible by the combination of the first and the second color materials, and wherein, regarding the color separation data for the color image at the hue of the special color: as a brightness of the input color image data decreases, the value of the color data corresponding to the color material of the special color is increased, decreased and increased again, in that order, and as the brightness of the input color image data decreases, the values of the color data corresponding to the first and second color materials is increased and decreased, in that order.