1. An image processing apparatus, comprising; a decomposing unit configured to decompose luminance of an input image into an illumination component and a reflectance component; a compressing unit configured to compress the illumination component; an extending unit configured to extend the reflectance component; a combining unit configured to combine a compressed illumination component and an extended reflectance component, to obtain a combined luminance; and an adjusting unit configured to adjust the combined luminance.