A luminance conversion function calculating circuit calculates a luminance conversion function in order that a specific image contained in an image represented by image data to be processed will be made to have a desired brightness. Saturation of the specific image in a case where the applied image data has been subjected to a luminance correction based upon the calculated luminance conversion function is calculated and upper-limit saturation is calculated based upon an input value from the user. If the saturation of the specific image after the luminance correction thereof exceeds the upper-limit saturation, then a target dynamic range revising circuit narrows the range width of a target dynamic range that stipulates the luminance conversion function. The luminance conversion function is revised in a luminance conversion function revising circuit so as to have the narrowed range width.