To provide an image processor capable of appropriately and easily controlling brightness, a color conversion method, a color conversion table preparation method, a program and a storage medium.

The image processor includes the processing of converting input color data expressed by an optional color system to color data that an image output device can reproduce. A first mapping means executes mapping maintaining the range of the brightness that the color data converted by an input color conversion means can take, and a second mapping means executes gamut mapping including the processing of compressing the range of the brightness that the color data mapped by the first mapping means can take into the brightness range of a color reproduction range A.