1. An image processing method of adjusting a gray axis of an image recording system in accordance with an image selected from a set of test images varying in color tone from one image to another, the method comprising the step of: adjusting a color tone associated with the gray axis by making a gradation adjustment separately for each ink color of the image recording system on the basis of the selected one image, wherein the plurality of images included in the set of test images are color images formed using a plurality of low saturation colors.