To provide a method for forming a proof image, etc. , capable of securing the proofing performance of a dot image by adequately reproducing printing nonuniformity to be generated in an actual printed matter and adequately reproducing even the dot shape of the printed matter.

The method for forming an area gradation image as the proof of a target printed matter with the use of the aggregation of images which are generated by combining a plurality of element colors where a density is independently varied includes: masking processing for determining a pixel to change the density of the element color in response to the printing nonuniformity of the printed matter; and output processing for generating the area gradation image, where the printing nonuniformity is reflected based on the masked area gradation image, with the use of a change look-up table which stores a standard element color density without the printing nonuniformity reflected thereon and a change element color density with the printing nonuniformity reflected thereon.