1. An image processing apparatus or processing color charts, said image processing apparatus comprising: a maintenance part configured to maintain color conversion information mapping each of a plurality of colors to a corresponding line pattern; a determination part configured to receive color image data for an image, determine a two-dimensional area of the image having a first color that is homogeneous in said two-dimensional area, and determine, based on the color conversion information maintained by the maintenance part, a first line pattern corresponding to the first color; and a processing part configured to modify the image by reproducing the two-dimensional area with the first line pattern in place of the first color, to generate a converted image, wherein the determination part determines that adjacent two-dimensional areas of the image include different shades of a particular color, and the processing part adjusts a line pattern corresponding to one of said adjacent two-dimensional areas, by increasing or decreasing the width of the lines in the line pattern.