Conventional technology does not permit adequate color adjustment easily for various kinds of images. This invention eliminates this disadvantage by outputting a preview image of the input image according to image data, acquiring information about unadjusted color which represents the color to be adjusted and which is contained in said preview image, causing the printer (printing apparatus) 20 to print more than one color among from the color and its neighboring colors represented by said information about unadjusted color based on the information about unadjusted color which has been acquired, specifying the information about adjusted color which represents more than one printed color as the standard information at the time of color adjustment, and generating the adjusted image data which expresses the adjusted image to be printed by the printer 20 from the image data based on the information about unadjusted color and the information about adjusted color. In this way it is possible to accomplish adequate color adjustment rapidly and easily for various kinds of images.