According to remarkable increase of color printing in newspaper and telephone directory, it becomes necessary to obtain same color reproduction for same photographs or advertisements printed by several printing factories distributed over the country. As several types of printing presses and plate making methods are used in the factories, it is difficult to obtain good color matching between the factories. In order to control color reproduction of this type large-scale printing system, paper and ink colors are standardized, then a standard tone reproduction curve proportional to L* of CIELAB are introduced. For each printing press, deviation from this curve is corrected by dot gain correction of output devices such as film setter and CTP setter.