How Many Colors Do You Need?

Most printers and print buyers are familiar with color bars used to maintain quality, but how many color patches do you really need? And which ones? How do we find the balance between not enough information and too much?

The four-color set: not enough.

The basic CMYK solids color bar many printers use is definitely NOT ENOUGH.  This is the rough equivalent of the crayons that are given to kids at the restaurant when they go out with their parents. Every kid knows that this skimpy selection is good for nothing more than scribbling on the paper tablecloth cover, and it is just about as useless for printing.

We don’t need to get too technical here. Everyone has seen press sheets with perfect CMYK densities that simply don’t match the proof in any way. That should really be no surprise, since most images have very little solid color image content. This is probably what caused many to feel that “running to the numbers doesn’t work.” Well, it does work, but not with that skimpy 4 color coloring set.

The eight color set: a little better.

The smallest official Crayola coloring box has eight colors. That is just enough to do some basic coloring activities, and can also give at least a rough idea of what is happening on press. The eight color set would include CMYK solids plus 50% tints of CMYK.  This yields a lot more information about the actual appearance. That is easy to understand, since most images are composed primarily of different tints of color.

The nine color set: better yet.

Adding just one additional color to the basic eight color patch set increases the usefulness of the color bar tremendously, if we choose the right color. A patch of CMY tints representing neutral gray is a component of the G7 specification, and is very effective. The logic is very simple. Most colors in real printed images are neither solids nor single color tints. Most are combinations of multiple tints. A three color neutral made of CMY tints is a good guide to what is happening when multiple tints print together. In addition, gray is one of the colors that the human eye is most sensitive to.

The twelve color set: getting better.

The twelve color set is probably the minimum that most  kids feel comfortable coloring with, and it is a good minimum for printers and print buyers as well. Adding red, green and blue to the patch sets takes advantage of an old pressman’s trick. Back before densitometers and all the rest, pressmen know that the red that you got by printing yellow over magenta was more important than either the yellow of magenta was alone. So they watched those three colors like a hawk.

The twenty-four color set: now we’re getting there.

We can finish up the process by adding 25% and 75% to our tints and gray patches and well as adding in 3 color solid an paper as well. That’s it. Twenty-four crayons would make any young Crayola artist happy, should do the same for any printer or print buyer.

Do we need the sixty-four color box with built-in sharpener?

No, not really. A color bar with 24 patches gives us enough information about press conditions to know with confidence how well our job is printing on press. And with easily available and inexpensive equipment and software, a 24 color bar can be read and deliver a full print quality report in ten seconds, letting us know instantly know if a print job meets specifications or not. No guesswork, no head scratching, no stressful onsite press OK.

Every kid loves Crayolas because coloring tells a story. With an adequate color bar and the ability to measure it quickly and easily, your color bar can tell a story too.

© 2014 Color Clarity

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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5 Responses to How Many Colors Do You Need?

  1. John Seymour says:

    Glenn, as usual, this is an excellent blog post. Thanks for sharing.

    I looked at this question scientifically, and came to a stronger conclusion, perhaps even a bit surprising of a conclusion. My results were published in a paper at TAGA 2011.
    (See pages 14 to 19 of this file: http://tinyurl.com/m5ao9x6)

    I had measurements of IT8 targets fro 100 newspaper printers. I looked at which patches best predicted the whole 928 patches in the set.

    If I took the four solids and the four 40% patches, I could do a good job of predicting the variation of only 20% of the 928 patches. If on the other hand, I looked at just two patches, the CMY 40% gray and a K40%, I could do a good job of predicting 28% of the 928 patches in the test target. Two patches are better than eight.

    My explanation is that there are three basic physical things that are varying on press: ink film thickness, dot gain, and trap. The solids are effected only by ink film thickness. If the dot gain of trap changes on press, you won’t be able to see it by looking at a solid patch.

    The halftone patches are effected by changes in dot gain and changes in ink film thickness, so they monitor more of the things that vary on press. Still, if there is a change in trap, you won’t see it if you are looking at just the solids and single ink halftones.

    The CMY gray patch is effected by changes in all three of those physical variables (at least for c, m, and y), so that patch gives us a good bang for the buck.

    • glenn says:

      Hi John, That is an excellent paper. I absolutely agree that if I had to choose only two patches, they would be the ones that you advocated: the mid tone black and CMY neutral. So why did I start off with CMYK solids and not get to CMY neutral until the 9 patch color bar? First, I wanted to start off on familiar territory; and just about everybody is familiar with CKYK solid patches, despite the fact that they are poor predictors of color on their own. Why not go straight to a 6 color bar with CMYK plus mid tone black and CMY gray? Just between the two of us, there seem to quite a few G7 skeptics who jump on every chance to start a gray balance debate and I didn’t want to encourage them.

  2. Hello John, Exquisite work in the 2011 TAGA paper. Thanks for DOING it, I hope some people are READING it.

    1.) We have been selling offset color control bars under the BETA EYESCAN COLOR BAR name for many years, first delivering them on film before CTP, and then as EPS files. Several unique features are incorporated into them, including “the right number of colors”. On a full-size offset press with 23 ink keys, we use 136 individual targets to give the press operator and QC technician everything they need to understand what’s happening on the press.

    The first feature of the color bars is the size of the individual patch. It makes perfect sense to US, but I’ve never seen it done on any other color bar. Each patch is one sixth the width of the ink key on the press. This is often 32.55mm or 35mm, or some other number in that range. We have a library of all presses that we’ve made targets for. In the width of one ink key we place FIVE targets, as follows;
    – CMYK solids
    – 50% visual gray balance patch

    This pattern is repeated in EVERY ink key zone without exception. The SIXTH target is one of the following;
    – RGB solid trap targets
    – 50% CMYK targets
    – 25% CMYK target
    – 75% CMYK targets
    – CMYK min/max dot (resolution) targets

    Obviously not ALL of these targets are of equal interest or importance, nor is every press wide enough to have enough keys to provide enough space to carry all these targets. Therefore they are distributed in a manner related to their importance and popularity with the pressman.

    – TRAP targets are centered on the bar, occupying the central 3 ink key zones, so no matter how few keys a press has, overprint solids will be present.
    – RESOLUTION targets are slightly farther left and right of center, occupying the central 9 ink key zones.
    – 50% CMY DOT GAIN targets require a wider bar, occupying 13 ink key zones

    No particularly big deal yet, but where are the 50% black targets? They are repeated every four ink key zones, and placed immediately adjacent to the CMY gray balance targets. This particular pair is prominently marked to catch the eye of the pressman, hence the EYESCAN moniker. For the wizened old pressman that “don’t need no stinkin’ densitometer” we provide an efficient and effective way for him to visually evaluate the press sheet.

    If he first prints a uniform black density across the sheet and visually verifies that the black 50% dot gain target is not flooded, he now has a neutral gray in every fourth ink key zone. This now serves as a reference for visual comparison of the CMY gray balance patch next to it. Under decent lighting, and barring worse than usual color vision deficiency, he now has setpoints and a sensitive detector of change on press.

    Imagine how much better he can do with a densitometer!
    – MEASURE the black solids across the sheet
    – MEASURE the 50% black tint
    – MEASURE the CMY solids
    – MEASURE the TRAP colors
    – MEASURE the CMY tints
    – WATCH the black/gray balance pairs. As long as they appear as a “double wide” patch with no readily discernable break, ALL of the related parameters CAN’T be very far off their target values. Changes in density will shift the gray balance, changes in dot gain will shift the gray balance. If the gray balance DOES begin to shift, all of the necessary diagnostic elements are there to determine the cause.

    Unfortunately too many press operators believe that “take-off bars” are all that’s needed to control a press. Dot gain is not of interest to them.

    2.) Gordon Pritchard published his findings on a related matter, concerning the usefulness of running gray balance targets ON HIGHLY GCR’d IMAGES. His findings were that they are NOT of much use, raising far too many false alarms.

    In complex color fields (not test patches) GCR and ink limiting are highly effective in helping pressmen run good-enough color most of the time. Solid densities were set initially and not changed unless they drifted outside of the tolerances.

    Non-GCR’d gray balance patches looked terrible and would have had the pressmen jumping all over the job, but the LIVE MATTER always looked OK. Gray balance targets are excessively sensitive in this case. The hardcore G7 guys were foaming, but Gordo held fast. Simple density-only control was sufficient.

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