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Summary:
In the past, at the Research Lab of the Royal Smeets Offset Company in the Netherlands, the quality control of a color electrophotographic analog proof was done visually every six months by three judges evaluating a proof of a gray balance chart. First, the tone reproduction curves of the four-colored proofs were evaluated by densitometry to insure good dot gain reproductions. Then, the nine shades of gray of the proofs (which are composed of fixed percentages of cyan, and varied percentages of yellow and magenta) were visually judged against a Kodak gray scale. This paper reports on research executed in the Winter of 1992 in which a spectrophotometer was used to control the quality instead of the above-mentioned method. Using the L* C* h (ab) system, the average C* values from each gray patch were compared and an aim point gray balance was selected on the assumption that the patch with the least C* values should be gray. This paper reports on research executed in the Winter of 1992 in which a spectrophotometer was used to control the quality instead of the above-mentioned method. Using the L* C* h (ab) system, the average C* values from each gray patch were compared and an aim point gray balance was selected on the assumption that the patch with the least C* values should be gray. The gray balance curves made by the conventional and spectrophotometric means were compared. It was found that the spectrophotometric method, linked to a computer measuring program (Lotus), is very successful and much faster than the conventional one.