Out of Gamut: Getting a Handle on Color Management

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Color management is a topic that continues to confuse, bewilder, confound, and even enrage all too many innocent users. This is due in part to misleading hype on the part of vendors that present it as a magic solution to all color problems, and in equal part to software developers who insist on making their implementation of color management different from everyone else’s. But if you understand what color management systems actually do, it’s a lot easier to see through the hype — and to decode the dialog boxes that pop up to annoy you in your favorite applications.

Color management systems really do only two things: They describe the color of pixels, and they change the values of pixels to keep the color consistent across different devices. That sounds simple enough, but anyone who has played the great Japanese game of Go can tell you that very simple rules can create an extremely deep and complex set of behaviors. And so it is with color management.

Color management systems were designed to resolve issues like “why doesn’t the image my scanner captures look like the original when I display it on my monitor?” and “why does the image displayed on my monitor look nothing like what comes out of my printer?” (If you’ve never suffered from either of these problems, you can skip the rest of this column, but we’d all like to know your secret!). To understand how color management addresses these issues, we need to look at what causes them in the first place.

The Problem
Computers don’t understand color. Fundamentally, they are adding machines that juggle ones and zeros on demand. When we started using those ones and zeros to represent color on computers, we did so by creating digital equivalents of the RGB (red, green, blue) or CMYK (cyan, magenta, yellow, black) analog signals used to control the various color-capable computer peripherals, such as scanners, monitors, printers, imagesetters, and platesetters.

RGB and CYMK are each systems that in essence allow three or four primary colors to be blended to create a desired color. The strength of each component signal determines how much of the corresponding primary color is used. When we adapted RGB and CMYK for representing colors digitally, we simply used numbers (8-bit numbers, which allowed 256 levels) to represent the strength of each component value.

This system works fine when you simply want to make a specific device produce a color. Unfortunately, when you send the same set of RGB or CMYK values to different devices, they typically produce different colors. RGB and CMYK represent control signals rather than specific colors, and each device responds differently to the control signals.

If you’ve ever watched a bank of televisions in an electronics store or peered down the length of a 757 during the no-doubt-engrossing inflight movie, you’ve probably seen this phenomenon in action: Multiple monitors, all receiving the same signal, produce different colors. Why? RGB values modulate the strength of the electron beam that makes the monitor’s phosphors glow, emitting light, and each monitor responds differently to the control signals. Different vendors use different phosphor sets, but that’s only part of the problem. The phosphors wear unevenly, losing the ability to emit light, and the monitor’s brightness and contrast controls, which are set by the user, have a huge influence on the color the monitor displays. It’s not unreasonable to say that each monitor is unique. (Which also means that the images used in this story to demonstrate my point will also appear different on your monitor than it does on mine, but even if the representations aren’t exact, I think you’ll get the idea.)

For slightly different reasons, the same holds true for all our other RGB and CMYK devices. Scanner and digital camera filters change with age and differ from model to model, as do the light sources they use. CMYK may be even more variable than RGB: There are many different formulations of CMYK inks, toners, waxes, and dyes, all differing in their colors, and when you bring the paper into the equation, you encounter another huge variable, given that different papers interact with the inks in very different ways.

You can think of RGB and CMYK as recipes for making color, with the distinct R, G, B or C, M, Y, K values being the ingredients. As any cook can attest, ingredients vary, and that variation affects the final flavor of the dish. So it is with color: Yes, you can be confident that, say, R255, G255, B50 will create a shade of yellow, but that shade will certainly be different on different devices.

RGB and CMYK are often called device-specific or device-dependent color models, precisely because they really only produce predictable results for a given device. This is the fundamental problem that color management seeks to address. The second, more-obvious problem stems from the first: Color changes when we send our files from one device to another, so the color the scanner sees doesn’t look like the color we see on the monitor, which in turn doesn’t look like the color that comes out of the printer.


Figure 1: The scanner sees the color sample as R247 G160 B91. But when we send the same RGB values to the monitor, it’s slightly darker and more saturated. When we send those same numbers to the printer, it’s much darker and even more saturated.

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Bruce Angus Fraser (9 January 1954 – 16 December 2006) was an author who specialized in digital color technology, including hardware and software for creating and managing color images and publications. He co-authored "Real World Photoshop" and others. He was a founding member of PixelGenius, LLC.
  • anonymous says:

    I enjoyed the article, but wondered why Bruce limited the color space to RGB and CMYK. He did not discuss Spectral Data. I would love see an article that explains the value of looking at Spectral Data.

  • anonymous says:

    Nice explanation of color theory but how about some step by step tutorials on actually managing color.

    Where do I start? What programs if any are needed? Will ColorSync alone do the job? How can I create profiles if none exist? Etcetera.

    I would like Bruce or someone to take me through step by step and tell me how to implement color management on my system. Or at least recommend a book or web site that details how to.

  • anonymous says:

    I’ll read more about color management as I have lots of questions.

  • anonymous says:

    Maybe it’s just too early in the morning, but Bruce really didn’t tell me how to do anything. So I can regurgitate the numbers, but for instance, I can’t embed a profile…
    not sure I gained anything but I’ll read it again. JD

  • anonymous says:

    People, I feel your pain. But the sad truth is that the step-by-step instructions you request are different for each application, and for each platform, and for each version of each platform. It would require a book, rather than a column.

    If you understand what color management is actually doing, you stand a decent chance of decoding all the (very) different dialog boxes in the different applications (and on the different flavors of the different platforms. If you just assimilate a set of step-by-step instructions, they’ll be good until the next time the app or the OS gets revved, then you’ll be back to square one.

    Color management is simple. That doesn’t mean it’s easy. I continue to bully vendors in an attempt to make it easier, but it’s not yet at the point where anyone can write a 12-step guide to getting good color, and anyone who tries would probably be eligible for a 12-step program!

    That said, I have posted, and will continue to post, step-by-step pieces too, but the only way to do that sensibly is to take a very specific color management scenario-importing an image from a scanner to a Photoshop working space, printing from a Photoshop working space to an inkjet printer, etc.

    I’m always looking for story ideas, so if anyone has a SPECIFIC color management question that’s addressable in about 1000 words, I’ll be happy to write the answer.

    For the bigger question, I AM working on the book, and hope to have it out in January ’02.

  • Anonymous says:

    This is definitely the best piece of information on colour management and profiles that I have come across so far in search of understanding the whole thing. I have read numerous others and they tend to either baffle reader with technology or oversimplify everything beyond boredom.

  • Anonymous says:

    MORE TUTORIALS

  • Anonymous says:

    In a last-ditch attempt to understand what in the world all the swirling words about color management meant, I stumbled across this article. It shouldn’t have to be said, but as a marker for other printmakers, here is a clearly, coherently, considerate piece of writing that teaches so well, QUICKLY, SIMPLY, even a physicist would have to admit color doesn’t have to be a dark hole of knowledge.

  • Anonymous says:

    In a last-ditch attempt to understand what in the world all the swirling words about color management meant, I stumbled across this article. It shouldn’t have to be said, but as a marker for other printmakers, here is a clear, coherent (not clearLY, not coherentLY), considerate piece of writing that teaches so well, QUICKLY, SIMPLY, even a physicist would have to admit color doesn’t have to be a dark hole of knowledge. (Was in a hurry to get in an autumn hike.)

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