An image processing apparatus for outputting an image by a printer or a display is provided, in which color reproducibility in the image output of plural pages becomes uniform. The apparatus comprises an image memory for memorizing image data of all pages of one output job that is given to an output device, decision portion for deciding whether the image data of all pages are data within a color reproduction range of the output device or not. A color compression process is performed for the image data of all pages uniformly only when it is decided that the image data of all pages are not data within the color reproduction range of the output device.