Using enhanced GCR (gray component replacement), it’s possible to use just three different screen angles in seven-color printing without risking color shifts. Black, as the dominant color, is assigned to 45°. The six chromatic colors, cyan, blue, magenta, red, yellow, and green, are alternately assigned to 165° and 105°. Then, each hue can be generated using only three colors: black, which provides the gray component; and two neighboring colors.
For example, all printable hues between red and yellow can be created using black and these two process colors. A maximum of 10% of a complementary color can be added to darken the color without causing color shift. Essentially, only three colors are printed on the same part of the image.
Sheetfed Offset Press Operating, 3rd Edition
Lean Printing: Pathway to Success
