The purpose of this study was to establish a reliable control method to maintain the visual hue consistency of "critical colors" on a four-color lithographic press. The term "critical colors" indicates those colors which are deemed by the customer or pressman to be important for a particular job and will require special attention to maintain their hue consistency. It was hypothesized that a densitometer, which automatically computes hue error and grayness using the Preucil method, could be used to measure critical colors and maintain their computed hue consistency. In order to analyze the effect of the control method monitoring hue error and grayness, the press sheets controlled by this method (the experimental group) were compared with the press sheets controlled by the pressman's visual judgment only (the control group). Colors with different hue and halftone-dot sizes were chosen as critical colors for the experiment. During the production of the experimental group, the hue error values of critical colors were controlled to remain within an arbitrary tolerance of ±4-percent from the measured hue error values on the O.K. sheet, as indicated acceptable by a previous study. From the sample press sheets drawn from the experimental group and the control group, the hue error and grayness values of each critical color were analyzed by three ways: (1) by the comparisons of standard deviation and mean; (2) by F tests; and (3) by utilizing the GATF Color Triangle. The experimental results in the F tests indicated that in most cases there was no significant difference in the variances of the hue error and grayness values of the critical colors between the two groups. However, the comparisons of standard deviation and mean, and the GATF Color Triangles indicated that in most cases the hue error and grayness values of the experimental group varied less and remained closer to the measured values on the O.K. sheet than the control group. It was concluded that a densitometer could be used to measure and monitor the hue consistency of critical colors. However, the control method monitoring hue error and grayness was not always reliable, because of the inconsistency of the relationship between calculated hue error and grayness values and the visual appearance of colors. For this reason, further analysis of the experimental data was made for saturation and ink hue using the GATF Color Hexagon. It indicated that saturation and ink hue as calculated and plotted were better monitors to be used for hue consistency than hue error and grayness. However, there was still a problem that the same saturation and ink hue values may produce different colors. It was suggested that monitoring the three filter density readings of critical colors would be a more reliable control method to maintain the hue consistency of critical colors.
Library of Congress Subject Headings
Printing--Quality control; Color printing
Department, Program, or Center
School of Photographic Arts and Sciences (CIAS)
Hashimoto, Chikashi, "Control of a four-color lithographic press by monitoring the hue consistency of the reproduction with a densitometer" (1979). Thesis. Rochester Institute of Technology. Accessed from
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