1. A color reproduction system for processing color image data supplied from an image input unit according to a color reproduction process depending on input conditions of the image input unit and output conditions of an image output unit, and reproducing a color image based on the processed color image data with the image output unit, comprising: conversion formula setting means for setting the color reproduction process as at least one image data conversion formula; variable setting means for setting a selectable variable conversion formula and parameters depending on the input and output conditions with respect to variables of said image data conversion formula; and selecting means for selecting said image data conversion formula, said variable conversion formula, and said parameters depending on the input and output conditions; the arrangement being such that the color image data are reproduced using said image data conversion formula, said variable conversion formula, and said parameters which are selected by said selecting means.