The following processes are performed when generating new image data by modifying the color tones of images in image data: First the user is allowed to select a parameter from a plurality of modification candidate parameters corresponding to mutually differing modification details; then, according to the selected parameter, modified image data in which the colors of at least a portion of the pixels differ from those in the subject image data, is generated. Note that when the subject image data is color image data, then the selection can be made from Nc color image modification candidate parameters, and when monochrome image data, the selection can be made from Nm (where Nm is an integer larger than Nc) monochrome image modification candidate parameters. This type of process can provide image processing that fulfill the needs of some users with the strict requirement while not complicating the operations performed by typical users.