1. An image processing apparatus for 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.