Color Patches for Beginners: A Process Control Primer (Warning: Not for Color Geeks)

 

Most of us are looking at a lot more color patches than we were just a few years ago, and we’re paying more attention to what we see; but which color bar is right? What are all these different color patches? Can’t we have a “one size fits all” set of color patches?

Not too long ago, the typical press color bar had four patches-one for each of the solid process colors. Today we see a wide variety of color bars for use on an equally wide variety of output devices, and they differ not only in the number of different color patches, but also in the information they are meant to convey: some are meant only to control elements of the printing process, others are focused purely on color verification.  (You can find a more detailed exploration of press control patches here). It can be confusing-so what’s going on?

Process, Predicted Result or Both?

Color bars can be grouped into two basic types, with an important degree of overlap in between. Typically, offset and flexographic presses use a color bar with a relatively small number of color patches that is used to control the process but which may be limited in its ability to accurately predict the final result. Profiled devices, such as many proofing or inkjet devices, on the other hand, may use color bars with a larger variety of color patches. These color bars can accurately predict  to the press operator for controlling the process.

As the industry moves in the direction of verified print quality, it is important to understand which color bars work best for each process, and which can provide helpful verification data. Let’s start with a quick listing of a few color bars you may have run into:

Pressroom Minimalism: the press density color bar

This is the simplest possible color bar. It has just the basics of Cyan, Magenta, Yellow and Black. It is obviously practical, can be scanned in just seconds, and is capable of giving a press operator needed direction for adjusting ink densities; but has absolutely no value predicting the final print appearance, or for giving the press operator more detailed information for controlling the press.

Speed: A+  Process control: D  Color Verification: F Best use: Closed loop inking system

Maximum detail: the IT8.7/4 Characterization Chart

In the US, the IT8.7/4 chart is the standard patch set for profiling. Its advantages are  obvious: it has LOTS of patches, so its accuracy in predicting the appearance of an image is very high. But it has far too many patches to read for process control, and it give no useful information to a press operator.

Speed: F  Process control: F  Color Verification:  A+ Best use: Profiling and press characterization

Verification First: the ISO 12647-7 color bar

 A very complete color bar, the ISO 12647-7 bar gives TONS of information from lots of different color patches…solids, tints, neutrals, and critical colors like fleshtones and pastels. This color bar can be accurate and very useful in verifying overall color accuracy, in terms of deltaE (average, maximum, percent out of tolerance, etc.), and is especially appropriate for verifying proofer accuracy.

The trouble is, with 84 patches this bar can still take time to read without automated scanning equipment, making it impractical for controlling color on a high-speed offset or flexo press.

In addition, while its wide variety of patches is very good for verifying overall color accuracy, many of the patches are unhelpful in giving the press operator direction for controlling the press.

Speed: C   Process control: C   Color Verification: A  Best use:  Proofing and profiled digital printing

Closing in on G7: The P2P Chart

The ubiquitous P2P chart is the standard chart for G7 qualification. It gives very detailed analysis of gray balance as well as primary ink solids, overprint ink solids, and a full range of tints, but doesn’t give the wide range of colors needed for profiling or proofer verification, and is too bulky for everyday use on a press.

Speed: D  Process control: C  Color Verification: A- Best use: G7 Qualification, NPDC curve creation

Effective Results in the Trenches: The enhanced press control bar

Speed: A   Process control: A  Verification: A- Best use: Press process control and color verification

The color bar most appropriate for controlling the process on an offset or flexo press is something I will call an enhanced press control bar. This type of color bar includes the basic CMYK patches on the old density-only color bars, but adds several elements from the P2P chart, in abbreviated form. It can be scanned quickly and when combined with appropriate software, can give the press operator detailed and practical information for controlling the process. And while it excludes some of the complex color patches on the ISO 12647-7 chart, it serves as a very good predictor of how these colors will reproduce, as we will see.

The enhanced press control bar typically includes these elements:

Solid CMYK patches for controlling density and tracking accuracy of the primary colors.

  1. Solid RGB patches. For tracking the accuracy of secondary colors and monitoring press conditions such as ink trap.
  2. Tints, for tracking TVI, or dot gain.
  3. Three color neutrals, for tracking and controlling gray balance.

These four elements represent things that the press and prepress and prepress teams can control directly. Knowing how the press performs in each of these key areas gives practical direction for maintaining the accuracy of the printing; and while this color bar does not include all of the colors of the ISO12647-7 bar, it does a very good job of predicting how these colors will reproduce on a printing press by reporting on the control points that influence these colors.

For example, while the enhanced press control bar does not include the browns and tan tones included on the ISO 12647-7 bar, it still does a very good job of predicting the accuracy of these colors on a press by reporting on the related colors that influence them. In this case, the browns and tans, which lie somewhere between neutral tints and red/orange colors, will be influenced by the same factors that affect these colors. In this case, red overprints will be very important, as will magenta and yellow tints, and gray balance. If these factors are under control on the press, the chances that our brown and tan tones will reproduce accurately are very high, even if we have not measured them directly.

Process control on a fast-moving press and color verification of a completed run are slightly different tasks; and the color patches ideal for each use may be slightly different. A well-designed enhanced press control bar combined with appropriate software gives useful information to both the press operator and the print buyer/brand owner, bringing their interests together and benefitting both.

I always keep my posts informative and product promotion-free. If you are a buyer, brand owner or printer interested in the subject of color communication, please check out my other posts and browse my website for more information on achieving effective prep-press collaboration. If you would like to learn more about process control and brand color verification with pressSIGN, please click here. Or contact me directly at glenn@colorclarity.net

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