1. A method of monitoring image quality in a multi-color printing process, comprising the steps of: printing two different three-color halftone control areas, each of the control areas consisting of overprinted cyan, magenta, and yellow halftones; measuring, with a densitometer the red, green and blue optical densities of both control areas; calculating the densities of the halftones of cyan, magenta and yellow ink from the red, green and blue densities of the first control area; calculating the densities of the halftones of cyan, magenta and yellow ink from the red, green and blue densities of the second control area; calculating the solid densities and dot gains of the cyan, magenta and yellow images from the densities of the first and second halftones of cyan, magenta and yellow, respectively; and monitoring image quality in the printing process based upon the solid densities and dot gains of the cyan, magenta and yellow images.