Color Essentials

Consistency for Viewing Color

One important method for assuring color consistency is to agree on standard lighting conditions for viewing color proof and press sheets. In order to reduce variables in color communication and reproduction process, the graphic arts industry has established standard color viewing conditions called a standard color viewing booth.
There are two things that make a color viewing booth special: the lighting (referred to as 5,000 K) and a neutral gray surround (referred to as Munsell N8 gray).
Viewing color in a viewing booth is important because the lighting conditions and the surrounding environment in which we view color will influence color perception. If there is no viewing booth available, the next best condition (closest to 5,000 K) is indirect sunlight.

Color when viewed under different lighting conditions will look different. Another issue with lighting and viewing color is metamerism, which occurs when two color samples appear to match under a particular light source, and then do not match under a different light source.
This is a strong argument for consistent lighting for color viewing. 5,000 K is used because it contains an even mix of red, green, and blue wavelengths. The lighting in the viewing booths is neutral for proper and consistent color viewing when approving a job.

How does the surrounding environment in which we view a proof or a press sheet influence the color? Adjacent colors, that is, colors that are adjacent to the proof or press sheet being viewed, can influence color perception.
This phenomenon is the “Adjacent Effect” and illustrates why it is important to use a neutral surround when viewing a proof or a press sheet. Munsell N8 gray is used for the surround color to eliminate the influence of the surround when viewing color.

Subtractive color refers to using Cyan, Magenta, Yellow, and Black inks on a white surround (usually paper) to reproduce full color. One component of the color reproduction process has the greatest influence on how good the color will look when printed on press: the paper.
The same ink color will produce very different results when printed on various paper types. The whiter the paper is, the greater the color gamut that can be reproduced on press. As paper becomes less white (and less expensive), the color gamut that can be reproduced on press becomes smaller.

A spot color is a term given to a special ink (other than Cyan, Magenta, Yellow, and Black) that is printed on its own unit of the printing press. There are many reasons why spot colors are used on a printed job. For example, when brand identification is important (such as Coca-Cola or Ford Blue), it is essential the corporate identity color is reproduced perfectly.
Another reason might be the use of Metallic Inks. Metallic Inks contain flakes of metal powder and produce printed content with a shiny, metallic luster.
Finally, spot colors are often used when the design calls for a color beyond the gamut of what CMYK (process color) inks can reproduce.

When images are converted from RGB to CMYK, the halftone dots for the Black ink are typically generated in one of two ways: using undercolor removal (UCR) or gray component replacement (GCR). This choice determines how much Black is introduced into the image, as well as how much Cyan, Magenta, and Yellow ink will be printed.
UCR reduces the amount of Cyan, Magenta, and Yellow and increases the amount of Black in areas where Black is already present. UCR primarily affects the shadow areas of the image and does not affect color areas. Images are more susceptible to color shift throughout the pressrun when images are separated with UCR.
GCR also reduces the amount of Cyan, Magenta, and Yellow and increases Black. However, GCR is more aggressive; it occurs when only Cyan, Magenta, and Yellow are present. Images separated with GCR tend to print more consistently throughout the pressrun, but can hinder the press operator’s ability to make color adjustments on press.

Describing color is difficult because it is a sensation; it’s as difficult to describe all of our other sensations: how something smells, tastes, or sounds, for example. Often, vague terms such as “flat,” “muddy,” “too warm,” “too cold,” or “needs more snap” are used to describe color.
For example, what if an image is too warm? Does “too warm” mean too red, too Yellow, or too Magenta? Does “too cold” mean too blue, too green, or too Cyan? “Flat” typically refers to lacking in contrast, while “muddy” typically means too dark. Using imprecise terminology will result in additional proofing cycles, delaying the production process.

What is reproduction? A reproduction is not an exact match; a reproduction is a likeness, or close facsimile. Printing is not an exact match process. This is because there are many color reproduction systems within the color reproduction process.
Photography is one example of a color reproduction system; proofing and pressrun are others. As we compare what the eye can see, to what photography can capture, to what the press can reproduce, the color gamut (or number of reproducible colors) is diminished.