To provide an image output system by which an image corresponding to arbitrary special colors can be outputted without necessitating an operator to set a color collection corresponding to the special colors even when the arbitrary special colors should be outputted.

A controller 3A stores a predetermined color collection in a color collection storing means B and previously stores a density table relative to combination of basic colors and several arbitrary special colors in a density table storing means C. Even when special colors which are not set in the color collection are included in image data received from image data editing terminals 1A-1C and RIP2 from a comparing and judging means A, a color collection corresponding to the special colors is prepared by using the combination of basic colors stored in the density table storing means C and a density table relative to the arbitrary special colors. Image data is outputted according to the color collection.