With advances in computer storage and electronic dot generation scanners a new color separation process has become possible. Although in theory the Gray Component Replacement (GCR) process has been possible since the early twenties, it has only recently been available through contemporary color separation methods. GCR is the process by which the gray component of a particular color reproduction is removed from the reproduction and replaced with black ink. The gray component is defined as specific combinations of the least predominant color and the other remaining inks. A printing form was designed to include three different color reproduction processes: the 100% GCR, 60% GCR, and normal chromatic. A standard color transparency used for color evaluation was included with a series of 24 color test patches. A colorimeter was used as the test instrument, and the color patches provided ease in measurement using the instrument. The form was mounted on the lithographic press and the press was run to match the proof. Once a color OK was obtained and samples obtained, ink densities of the other units were selectively varied to provide a shift in hue. A colorimeter was used to obtain a value of Delta hue from the selected press sheets. Each standard color press sheet was measured and recorded as a standard with successive readings measured in terms of Delta hue. The color test patches were divided into groupings of neutral gray, hard to print, process/overprint, and all colors. Each Delta hue measurement was recorded and grouped into the specific categories. The variations of the normal chromatic and the 100% GCR separations were compared, as well as the variations of the normal chromatic and the 60% GCR process. This is to say that the neutral gray color grouping compared the measurements of the 100% GCR to the measurements of the normal chromatic process. These same measurements were taken for each variation within each color grouping. Delta hue readings for each of the color groupings was used to calculate a t-value and test the significance of the difference between the different processes. If there was indeed a difference between the different processes then a t-value of 1.65 would result. A level of significance of .05 was obtained in all of the comparisons. The GCR does reduce shifts of hue on the lithographic press. This reduction in shifts of hue should relate to an increase use of the GCR process in the future.
Library of Congress Subject Headings
Color printing; Color separation
Print Media (MS)
Department, Program, or Center
School of Media Sciences (CIAS)
Kellogg, Hans P., "The effect of solid ink density on shifts in hue in gray component replacement" (1987). Thesis. Rochester Institute of Technology. Accessed from
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