Why LCD televisions run the gamut

Jan. 1, 2009
It’s not a word that I would use in everyday speech but if I wanted to impress you with my fancy vocabulary, I might say, “English cuisine runs the gamut from awful to appalling.

I have yet to invest in a snazzy new flat-panel high-definition television set despite the nose-bleeding roller-coaster prices exhibited recently during the intense shopping period between the two major holidays of Thanksgiving and Christmas. Frankly, this is not a matter of getting more bang for your correspondent’s buck, but rather a question of my initially futile attempts to sort out the technical specs (as any good engineer is bound to want to do, Right!).

The basics are easy, of course, such as screen size and weight, whereas the audio/visual specifications are often arcane. And can I assume that most of you will be familiar with the resolution criteria of 720i, 1080p, and so on? And you do understand the relevance of the word “gamut,” don’t you? It’s not a word that I would use in everyday speech but if I wanted to impress you with my fancy vocabulary, I might say, “English cuisine runs the gamut from awful to appalling.”

But, wait a minute. What is the true meaning of “gamut” and why should we care about it when shopping for a flat-panel LCD? My old and battered yet still faithful dictionary (Merriam-Webster’s Collegiate, 10th Edition) says, “1. The whole series of recognized musical notes; 2. An entire range or series.” That doesn’t help me very much. So much for faith.

Well, it would appear that the word has been adopted or hijacked, if you prefer, by people who make high performance-color displays and similar equipment. Color gamuts are often represented on three-dimensional chromaticity diagrams. I don’t have room to show you one in this column but you can Google the term and you will get a selection of nifty chromaticity diagrams to puzzle over. But, I digress. What on earth does gamut have to do with LCD panels?

Quite a lot, as things turn out. The de facto standard for gamut is derived from the familiar NTSC color television specifications. For CRTs, the color model is usually the familiar RGB (red-green-blue) model. For four-color printing (as in this magazine), a different model is used, called CMYK (cyan-magenta-yellow-black).

For LCDs and color printers, the “holy grail” is the ability to reproduce the entire visible color space—the “color gamut” in engineering terms. LCD screens filter the light emitted by a backlight so the gamut is limited to the spectrum of the backlight. Until recently the backlights were often cold-cathode fluorescent lamps (CCFLs) but higher color gamuts can be achieved with high-intensity LEDs.

So now you see why gamut matters when you are buying an LCD monitor. It’s all about saturation. Color gamut is usually expressed as a percentage of the NTSC color space standard—100% is very good and 133% is outstanding. However, color is a matter of not only the quality of the display but also the eye of the beholder. You may find, as I did, that intensely saturated colors are overpowering for your eyes. In such a situation, individual color saturation controls are invaluable.

None of this will improve your digital HDTV viewing unless your incoming signal is also of high quality. That’s too complex a topic for this column, but I would recommend you take a look at “Resources for You,” on the Tektronix website (www.tektronix.com). You might also invite your cable guy in for cocktails.

If you would like to look beyond color gamuts for television, I would recommend, as a starting point, a rather slim book by Jan Morovic, entitled Color Gamut Mapping, (one of the titles in the new John Wiley-IS&T Series in Imaging Science and Technlogy). Morovic is a senior color scientist with the Hewlett-Packard Co, Colchester, England, and an expert in “cross-media” applications. Morovic’s book illustrates the range of possible gamut mapping strategies for cross-media color reproduction, evaluates the performance of various options and advises on designing new, improved solutions. Starting with overviews of color science, reproduction, and management, the book includes several useful mapping algorithms. But, be warned, this book is not for the rank beginner!

About the Author

Jeffrey Bairstow | Contributing Editor

Jeffrey Bairstow is a Contributing Editor for Laser Focus World; he previously served as Group Editorial Director.

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