Color Gamut Explained

Color Gamut Overview

You may want to check out my article on how LCD TVs work to better understand what will be talked about here. Moving on, a color gamut, color space, or color range are a subset of colors that can be produced by a display such as a PC monitor or TVs  in this case. It’s important to note that it’s actually the colors they can produce in certain environments. Similar to how contrast ratio is determined in a real living room versus a controlled environment, I test the color gamut in a real living room. Though not entirely related, but a color gamut or color range could be used to describe a photo that has been printed. It also has a color gamut that is static and unchanging.

Another huge thing to remember is that a purely realistic color range that covers the entire visible spectrum is currently not possible. Engineering hurdles and technological leaps need to be made to realize this goal. With that being said there are tons of different colors gamuts with different uses. The most common being the RGB color gamut. This is good to remember as with different gamuts there are different areas that will be covered by those same gamuts. The RGB can produce a very close to pure red color while the CMYK gamut cannot.

To express this further I’ve listed many of the colors gamuts below and their uses.


 color-gamut-trt
What it is: Range of colors a display or TV can produce.
Why it matters: Scenes look more accurate and detailed.
When it matters: Mostly HDR content. Many newer Blu-Ray movies are HDR ready.

Different Color Gamuts

RBG RGB stores individual values for red, green and blue. RGBA is RGB with an additional channel, alpha, to indicate transparency. (Common color spaces based on the RGB model include sRGB, Adobe RGB, ProPhoto RGB, scRGB, and CIE RGB.)
CMYK CMYK stores ink values for cyan, magenta, yellow and black. There are many CMYK color spaces for different sets of inks, substrates, and press characteristics (which change the dot gain or transfer function for each ink and thus change the appearance).
YIQ Formaly the NTSC, this system stores a luma value roughly analogous to (and sometimes incorrectly identified as) luminance, along with two chroma values as approximate representations of the relative amounts of blue and red in the color.
YPbPr Similar to YIQ. It is most commonly seen in digital work.
YCbCr Widely in video and image compression schemes such as MPEG and JPEG.
xvYCC A new international digital video color space standard. Similar to Rec.709, but a little larger.
HSV (hue, saturation, value) Often used by artists because it is often more natural to think about a color in terms of hue and saturation than in terms of additive or subtractive color components.
TSL  (Tint, Saturation and Luminance) Mostly used for face detection.
DCI-P3 A common RGB color space for digital projection. Think of this as a standard that most TVs should have everytime the TV is tested.
Rec. 709 Most commonly known by the abbreviation BT.709. Holds the format of high-definition television.
Rec. 2020 Most commonly known by the abbreviation BT.2020. Holds various aspects of ultra-high-definition television (UHDTV) with a standard dynamic range (SDR) and wider color gamuts (WCG).


Though there are many different colors gamuts with their many uses, the ones we will focus on are the DCI-P3, Rec. 709, and Rec. 2020 color gamuts.

How to Test Color Gamut

A color gamut is measured using a saturation sweep that samples six main colors that stress the display or TVs ability to produce those same six colors. The six colors are red, green, blue, cyan, magenta, and yellow. Then those same six colors are tested at five saturation levels which are 20%, 40%, 60%, 80%, and 100%. By doing this it allows for a thorough test that will provide accurate and realistic information.
After a good test on a good TV you should expect the colors ranges to look like the following:

hue-saturation-trt

  • DCI-P3xy > 90%
  • DCI-P3uv > 90%
  • Rec. 2020xy > 90%
  • Rec. 2020uv > 90%

Anything less than the above scores means the color gamut of the Tv are lacking. Though a little under the preferred scores are alright, but too far under and you will have some noticeable color range issues.

Wide Color Gamut

Color GamutRec. 2020 defines two resolutions of 3840 × 2160 (4K) and 7680 × 4320 (8K). Though, primarily I will only worry about the gamut of a 4K quality test as TVs are not readily available with 8K quality.

Rec. 2020 also specifies the following frame rates: 120p, 119.88p, 100p, 60p, 59.94p, 50p, 30p, 29.97p, 25p, 24p, 23.976p. This is important to remember as color gamuts that are not wide do not specify frame rates that are over 60 frames. You are covering much more ground here if the TV can produce a color range this large.

Similar to the RGB and the CMYK color gamuts I spoke about ealier, the Rec. 2020 contains colors that the Rec. 709 color gamut cannot produce. Since most TVs can produce most of the Rec. 709 color gamut, testing the Rec. 2020 gamut is a much better test that will produce more tangible results.

The primary use of the wide-color gamut is for HDR content that required more resources to not only look well, but also run smoothly. Many Blu-Ray movies are coming HDR ready and many streaming platforms are producing HDR ready content as well. By having the necessary tools ahead of the curve means adding life to the life-cycle of your TV. Though, often overlooked, that’s always a good thing.

Some of the most popular TVs right now actually have a wide-color gamut if you are interested. Such as the Sony X900E, LG B6, and the Samsung KS8000. Check out these TVs if a wider color range is important to you.

Conclusion

A color gamut can be very basic and small while at the same time very large and complex. Very simple tests can be ran to find the best results of your TVs color gamuts. Though I prefer to test only the DCI-P3 and the Rec.2020 color spaces, you can go ahead and test any and all that you see fit. Remember though a color gamut that you test may be lacking, that does not mean it is bad.
Hope this helps iron out some of the kinks with color gamut.

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