A state transition display window displays a hue circle and a number of setting points corresponding to respective color adjustment levels. As the user makes color adjustments, a history of the color adjustments is displayed in the form of arrows connecting related setting points. If the user specifies two setting points, images corresponding to setting point located on the line connecting the two specified setting points are displayed on an image display subwindow. A current image and six images adjacent thereto are displayed in a 6 near images display window.