Association Insights: Gray Component Replacement - A Primer

Implementing the G7^® specification is ideal for achieving gray balance and visual similarity across all print processes. This process provides accurate, predictable color from proof to press. What should not be overlooked, however, is the notion of maintaining consistent color balance throughout the pressrun. Have you ever had a customer fan out a job, revealing that the colors don’t match from sheet to sheet? We have all had to deal with this problem at one time or another. This article can be used as a primer to better maintain color consistency and repeatability throughout a pressrun.

The ability to maintain consistent color of images during the pressrun begins with the color separation process. Converting images from an RGB or LAB to the CMYK color space is not as simple as a mode change in Photoshop. Considerations must be made for ink, paper, and the condition of the press, to name just a few.

Color reproduction considerations

Gray component replacement (GCR) and undercolor removal (UCR) are color reproduction considerations for the printing press. UCR and GCR determines how much cyan, magenta, and yellow are replaced with black within a CMYK image. UCR and GCR may be incorporated into CMYK color separations during the conversion process.

UCR reduces the amount of cyan, magenta, and yellow primarily in the shadow areas of an image, while increasing the amount of black ink. UCR affects primarily the neutral shadow areas of the image and has no effect on the color areas of a printed reproduction. UCR was designed to help alleviate potential printing problems associated with heavy ink coverage, such as set-off or blocking.

Gray component replacement also reduces the amount of cyan, magenta, and yellow in a printed reproduction. However, GCR is more aggressive as it affects the neutral and color areas throughout an image. GCR replaces the gray component of the trichromatic colors with black during color separation. A trichromatic color is any color that is made up of all three of the primary printing colors cyan, magenta, and yellow. The gray component of the trichromatic colors is the level to which all three primaries are equally present. Applying GCR replaces the gray component of trichromatic colors within an image with black ink only.

Since GCR introduces black anywhere there would have been cyan, magenta, and yellow in an image, a GCR separation will print more consistently throughout a pressrun. And, becuase cyan, magenta, and yellow inks are replaced with less expensive black ink, a real cost savings can also be realized with GCR.

The major benefit of GCR is maintaining image color consistency during a pressrun. This benefit can also be a disadvantage as GCR reduces the ability to make color adjustments on press. If you deal with customers who insist on making the press operator “correct” color during press checks, GCR may not be the best option.

Keys to using GCR

• GCR improves color consistency on press. GCR separations will produce more consistent, repeatable color throughout a pressrun. The disadvantage of this, however, is the reduction in the ability to make color changes on press.
• GCR reduces ink costs. Cyan, magenta, and yellow are reduced within an image and replaced with less expensive black ink.
• More GCR results in more black within an image. Since most text on a press sheet is black, densities are often run higher, which can adversely affect GCR separations.

Learn more 

Managing color crosses many organizational lines—from design to brand management to production. The objective is to maintain color brand integrity across product lines while using diverse production processes. There is no better event to learn everything there is to know about doing color right—and making this happen—than the 2018 Color Conference, hosted by Printing Industries of America, January 13-16 in San Diego, California. Visit www.printing.org/color for more information.