TV tech terms demystified, part three: Color standards and definitions

Color accuracy went south at the introduction of LED-backlit LCDs, due largely to the extreme skew to the blue end of the spectrum that early backlights were prone to. Fortunately, the TV industry has made significant strides since then. The latest mid-range to high-end LED-backlit LCDs produce noticeably more accurate color than previous generations. In most cases, they rival—and in some cases surpass—OLED. If you want reds that are actually red, not dark orange, the newest TVs deliver.

In this, the third installment in our series that cuts through the BS routinely used to market new televisions, we explain the terms, standards, and specs involving color. If you missed the first two installments, you’ll find our discussion of screen size, resolution, and refresh speed here, and our explanations of display types and technologies here. Our final installment is an in-depth exploration of LED backlighting technology.

Vendors tout their TV’s color reproduction in many ways: bits, billions of colors, and so on; but numbers only describe general capabilities, not how accurately colors are mapped (i.e., changed to the closest possible color that can actually be generated) and produced. When it comes to color, use your eyes as the specs are seriously difficult to decipher. That said, higher numbers are better, if not a guarantee.

RGB (Red/Green/Blue): These three colors combine to form the other colors in the spectrum. With TVs, one red, one green, and one blue subpixel make up each pixel. This is done by varying the intensity or luminance of each dot in the trio. Occasionally, a white subpixel is added to a pixel to increase brightness (WRGB). There’s also a method we call subtractive WRGB that increases brightness, but decreases resolution. Your TV’s advanced settings might offer color adjustment via red, green, and blue levels.

Color depth (aka bit depth): The number of bits in a digital video signal that are used to indicate the color component of a single pixel. With 8-bit color, there are eight bits for the red component, eight bits for green, and eight bits for blue. With 10-bit color, there are 10 bits for each pure color, with 12-bit color there are 12 bits per color, and so on. You might also see color depth described in terms of the total number of bits: e.g., 24-bit color (8 bits times three), or 30-bit color (10×3)

12- and 16-bit color are coming into play. Dolby Vision supports the latter, and it can make for more accurate mapping, but we’ve yet to run across a consumer-grade 12-bit panel, let alone a 16-bit panel. (See also: Deep Color and True Color, below.)

Color space: The range—or gamut—of colors a video display can produce. There are various color-space standards, but the ones most commonly associated with TVs are—from narrowest to broadest—sRGB, from Rec.709 (part of the HDTV spec); Adobe RGB; and Rec.2020 (part of the Ultra HD spec). Vendors will say their TV meets N percentage of X space (90 percent of Rec.2020, for example)..

Nanosys, Inc.

Chroma sub-sampling 4:4:4 (4:4:2, 4:2:2, etc):You’ll normally run across these numbers when you see which resolutions and signals can be transmitted via your TV’s HDMI ports. As these ports can be bandwidth limited (read this article comparing HDMI to DisplayPort for the details), color depth can be compressed to fit a signal into the bandwidth that’s available. We’d be here all day explaining the variations, but 4:4:4 means no color reduction. Lower numbers in the second or third position mean that there is. A more detailed description is available on Wikipedia if you want to get into the weeds. These numbers are only significant if you’re using optical disc players or external streaming devices.

Deep Color: A digital video signal supporting Deep Color uses 10-, 12- or 16 bits for each of the red, green, and blue components of a pixel to deliver billions of colors. The HDMI spec supports Deep Color starting with HDMI 1.3. Note that you’ll also see these described as 30-bit, 36-bit, and 48-bit color (3 times 10, 12 or 16) (See also: Color depth, above.)

High dynamic range (HDR): This simply means a greater distance between the brightest tone and the darkest tone that a TV can produce. This can be achieved by increasing brightness (the most common tecnique) or making dark areas darker. The latter is difficult for LED-backlit LCD technology, but it’s easy for OLED and micro-LED because those displays are self-luminous—they can create a black pixel by turning off the power to that element. You’ll see HDR marketed as X-Tended Dynamic range (Sony), Ultra Luminance (LG), or even the ostentatious Peak Illuminator Ultimate (Samsung). You can read a deeper exploration of high-dynamic-range TVs here. (Note: HDR in photography is the same effect, but cameras produce it by combining images with different levels of exposure.)

HSL (hue/saturation/luminance): Another way to refer to, and in your TV’s advanced settings, adjust colors. Put simply: hue is the color, saturation is the richness of said color, and luminance (or brightness) is how bright or dark it is.

Adobe RGB: A color standard/color space implemented to match roughly the spectrum attained by the paper-and-ink world’s CMYK (Cyan, Magenta, Yellow, and blacK). TV vendors will use Adobe RGB as a point of comparison, which is fine for HDTV and 8-bit panels; but for 4K UHD and newer 10-bit panels, look for comparisons to Rec.2020. Adobe RGB covers more colors than sRGB, but fewer than Rec.2020.

Rec.2020: An abbreviation of ITU-R Recommendation BT.2020 (ITU is the International Telecommunications Union). Rec.2020 also deals with resolution and frame rates, but you’ll generally only see it mentioned as a color standard. When you hear a vendor say its TV reaches 98 percent of Rec.2020, it means the TV can reproduce 98 percent of the colors in that standard.

Rec.709: Another ITU standard, but this one defines the resolutions, frame rates, and other specs for HDTV that encompass the sRGB color space (see below).

sRGB: The original color space for computers and color displays as defined by Rec.709. This color space is slightly smaller than the Adobe RGB color space, and it’s considerably smaller than Rec.2020.

True Color: 8-bits per subpixel, 24-bit total color depth. A digital video signal supporting True Color uses 8 bits for each of the red, green, and blue components of a pixel to produce 16,777,216 colors. (See also: Color depth.)

Don’t miss the other three installments in this series. In part one, we cover screen size, resolution, and speed; part two goes over display types and display technologies; and we wrap up the series with the lowdown on LCD backlighting tech.