Ultra HD 4K TV color, part I: Red, green, blue and beyond

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Since the first color TV signals were broadcast, over 50 years ago, there have been shockingly few advancements. Thanks to limited bandwidth, legacy standards and the limitations of ancient CRT televisions, even the HDTV standards introduced in the early 2000s didn’t improve color realism much beyond what had been possible for decades.

That’s all about to change. In one of the most exciting advancements since high-def itself, new color standards are on the horizon that aim to improve the color accuracy and realism of next-gen televisions.

But first, we need to talk about color, and why it’s important.

There’s a lot to cover, so we’re breaking this into two articles. In this first part, we’ll discuss the nature of color and how color works on TVs. In Part II we talk about the future of TV color, and where it’s headed.

Let’s talk about color, baby

There are two types of primary colors: additive, and subtractive. Subtractive primaries are what you find with fingerpaints, tie-dyes and, well, any other paints and dyes. As any school kid knows, these primary colors are red, yellow and blue.

Except…that’s not really accurate. Modern color theory (and what’s used in printing and elsewhere that requires subtractive color), shows that magenta, yellow and cyan are the best colors to use in a subtractive color setup. Go into any magazine’s art department (if you can find any), and they’ll be using CMYK (the “K” stands for for Key, which in this case means black).

We don’t really care about subtractive color, since this is a tech website — albeit one that publishes a print magazine — and you are viewing it on a display that uses additive colors. Additive colors are the blending of actual light, where subtractive is the adding of pigments to subtract (absorb) all the wavelengths of light except the color you see (add vs subtract!).

Additive color primaries are red, green and blue. I bring all this up because every time I write “primary colors” and RGB in the same sentence, someone tries to mansplain that “everyone” knows the primary colors are red, yellow and blue. Nope. At least, not in this context.

Blending light is important, because it’s how every color TV, monitor or screen you’ve ever seen creates colors beyond red, green and blue. Add red and green together, you get yellow. Add green and blue together, you get cyan. Added blue and red together, you get magenta. Add different amounts, and you get different shades.

As I’m sure you’ve keenly noticed, blending primary colors together creates “secondary colors,” and the secondary additive colors are the primary colors of subtractive color (and vice versa). I love it when things are so simply symmetrical.

You know what? This is a lot easier if I show you. Venn diagrams for the win:

The big question

So what is red? Or green or blue, for that matter?

The scientific answer is a specific wavelength of light we call those colors. But the vagaries of the term are something best fixed with a Pantone vocabulary. For example, if I ask you to think of something “red” do you think of the red of an apple or the red of a fire truck. How about the CNET red on this very page? Aren’t Chili red, Brick red and Crimson all…red? They are, but which one do I mean? Thatis the problem.

My point is, saying something is “red” is like saying it’s “big.” It needs more description.

If the TV world was this level of vague, it would be anarchy. Human sacrifice, dogs and cats living together…mass hysteria! CBS’s red would be different from NBC’s red, which would be different from Fox’s red. So if your TV was set up to watch one, the other would look wrong and weird.

Thankfully, it isn’t. The HDTV color standard is called Rec.709, and it stipulates the exact red, green and blue primary colors, and yellow, cyan and magenta secondary colors, that every broadcast and television should (and usually do) conform.

As an aside, your TV likely doesn’t display these colors correctly out of the box, but most new TVs, in the Cinema or Movie mode — or in the Standard color mode — will show the colors the way the people who make the content intended. Check out Getting the Best TV Picture for more info.

Unfortunately, Rec. 709 is ancient. It’s rooted in the technological limitations of CRT televisions, which weren’t exactly new when HDTV came out and haven’t been seen much (or at all) in a decade. 709 is OK, but there are plenty of colors the human eye can see but that aren’t reproducible by an HDTV. Truly deep red, green and blue just aren’t possible, and without them, all the other colors are limited as well.

Since we’re getting a new resolution standard known as 4K/UHD ( whether we want it or not), now would be a great time to update our color system as well.

And, mercifully, that seems to be exactly what’s happening. All the major TV manufacturers are discussing wider color gamuts and greater bit-depth. These two things will greatly improve the color accuracy. We’ll get into that in Part II.

In your TV (and why accurate color matters)

How this works in your TV is the same, regardless of what technology you have. In fact, better than I can explain it, just stick your face close to the screen. Closer. Even closer! Don’t worry, no one’s watching or judging (nah, just kidding — of course they are).

As you can see from up close, each pixel is actually made up of three sub-pixels, one each for red, green and blue. By varying the amount of light you see from each, a whole rainbow of colors appears.

Who cares about accurate color? Well, the importance of using the best color setting can be seen in the following images. Which one is correct?

The correct answer is whatever one the photographer (in this case, me) intended. The top image, though not as colorful, is actually the most realistic representation of the actual road. Bonus points to anyone who can guess the location within 500 miles.

Or how about this: which of these is correct?

In this case, the entire landscape changes (again, the browner one is correct). So if a director intends for you to see a dying landscape of brown bushes, but your TV twists that to lush green shrubs, that’d be bad, right? Yeah, this is an exaggeration, but hopefully you see my point.

A word on extra yellow sub-pixels

Sharp, for the past several years, has touted an additional sub-pixel: yellow. The idea is for a better yellow, and by extension, additional colors. Except there’s no content to take advantage of this. So the TV has to “invent” the additional yellow. That’s not ideal.

In CNET’s testing, the technology has never lived up to the hype Sharp throws at it. In fact, in some cases, the odd sub-pixel structure can be visible (depending on where you’re sitting, and how big the screen is), creating an odd “crenelation” effect to certain lines.

Bottom line

While it’s not quite as important to an impressive picture as contrast ratio, accurate color is a crucial part of a television’s image quality. Ideally, it supplies lifelike images that look exactly like the production team intended. Beyond that, they look realistic, less like “watching a TV” and more just gazing through a window.

We’ve been stuck with relatively limited color reproduction in televisions, but that’s about to change. We’ll look at the future of color in Part II.

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Got a question for Geoff? First, check out all the other articles he’s written on topics like why all HDMI cables are the same, LED LCD vs. OLED, why 4K TVs aren’t worth it and more. Still have a question?Send him an email! He won’t tell you what TV to buy, but he might use your letter in a future article. You can also send him a message on Twitter @TechWriterGeoff or Google+.