1. An image processing apparatus comprising: a) input means for inputting color image data which is compression-encoded in a color difference system color space; b) decoding means for decoding the color image data input by said input means; c) processing means for executing correction processing for luminance component data of the color image data decoded by said decoding means; and d) encoding means for encoding the luminance component data processed by said processing means, and color difference data of the color image data decoded by said decoding means.