PROBLEM TO BE SOLVED: To reproduce a paper color of printing paper for a printing machines, and reproduce expression characteristics of black ink on a print material, in proof print. SOLUTION: Among image data for proofing throughout a subtractive color mixing space, which is obtained by color matching of a proof obtained by a proofing machine and a printed material obtained by the printing machine, image data for proofing which expresses on the proof each stage of gradation of a black monocolor on the printed material, having a portion of the printing material having a black ink area ratio of 100%, is expressed using only black ink on the proof, however, the portions of the printing material other than the 100%-black ink area ratio portion are modified so that they are expressed on the proof, using an under color removal operation, thereby reproducing on the proof the expression characteristics of black ink on the printed material. COPYRIGHT: (C)2007,JPO&INPIT