gray component replacement (computer graphics) (GCR)

Gray Component Replacement(GCR), like Under Color Removal ( UCR), is a color conversion model for reducing ink coverage and drying time of the print. As can be seen from the name, it involves replacing the gray component.

In the GCR process, to print gray, the colorscyan (C), magenta (M), and yellow (Y) are not printed, but are replaced with depth (K). This color set ranges from white to a gray value of over 50%. Here, the depth component (K) increases approximately linearly from 0 to over 90 %, after which it becomes non-linear. Only at brightness values above 60 % are the printing colors cyan, magenta and yellow added to the black component. For example, a gray with a brightness value of 50 % according to the GCR process consists of 50 % black and 1 % each of the printing inks. Only at higher brightness values does the cyan proportion increase disproportionately compared to the other two colors.

Characteristic curves of the colors and depth (K) in the GCR process

In addition to the advantages already mentioned, this also has the advantage that the sensitive gray tones are easier to print than if they were composed of the three printing inks, which can lead to color casts.