In an image display unit which applies a desired image processing to inputted image data and then displays the processed image, reflection characteristics for each color component of an output provided from the image display unit and reflected by a predetermined projection plane and by a reference projection plane are measured. Further, a correction curve is generated for correcting the inputted image data so as to eliminate a difference between the measured reflection characteristics for each color component reflected by the predetermined projection plane and by the reference projection plane. With the correction curve, an image processing is performed for the image data inputted to the image display unit, taking into account the characteristic of the projection plane on which an output from the image display unit is projected.