When producing gray values with four ink colors, substantial savings can be realized by replacing portions of the Cyan, Magenta, and Yellow with black ink. Two methods are used to do this, Under Color Removal (UCR), and Gray Component Replacement, (GCR).

With UCR, a single black ink is used for any shade of gray produced by C+M+Y in shadow portions of an image. GCR goes a step further and substitutes black for equal components of C+M+Y in any portion of the image. With this 1-for-3 replacement, ink use is reduced by 2/3 for this portion of the image. The black used is less expensive than the replaced colors, easier to recycle, and more plausible to be a recycled ink itself.

Less ink coverage allows for easier gray balance, better run stability and color consistency, faster make-ready, more consistent and faster ink drying and faster printing. The images produced show cleaner and more consistent colors, improved detail and sharpness.

Author: John Coburn, SGIA
Source: SGIA Journal, Q1 1999, p. 7-10.