The “image enhancement with luminance preservation” is a self-conflict proposition. Researchers, including propositional proposer Kim, gave the index AMBE (absolute mean luminance error) to judge if the “luminance preserving”, however, which just proved that the image enhancement with “luminance preserving” cannot be realized. We have proved that the visual quality of an image is a function of the image average luminance with convex feature. The image cannot be enhanced with luminance preservation, and the luminance cannot be preserved with image being enhanced. The visual perception quality of an image is not equal to the image contrast. We can experimentally prove what the higher the contrast of the image, the better the visual quality of the image is not true.