Lately we have seen TV manufacturers increasingly advertise the color gamut of a TV. Terms like Wide Color and DCI-P3 are often mentioned, but what exactly do they mean and what is the use of them as a viewer? In this article, we will list everything about the color gamut of TVs for you.
The color gamut of TVs
Color, we associate it with emotions, places, environments. Not only the color itself, but also dark or light colors, bright or soft colors, it all plays a role. Color is therefore a not to be underestimated part of the arsenal of possibilities that a director uses to evoke a certain atmosphere.
But correctly recording color, saving it during editing, and displaying it on a display is more difficult than you think. International standards are very important to ensure that this runs smoothly. For example, all colors that the human eye can perceive can be found on the CIE 1931 chromaticity diagram.
However, no display can display all those colors. That is why subsets of all those colors are also defined, which we then call a color range or color gamut. A color range is defined by three basic colors, red, green and blue, and a white point. It includes all the colors that fall within the triangle of those base colors on the chromaticity diagram. The more pure those base colors, read closer to the outer edge of the chromaticity diagram, the larger the triangle and thus the color range. Content, such as films and TV broadcasts, is adjusted during the mastering process so that all colors fall exactly within one specific color range. And displays are also designed to conform to at least one standard color gamut.
Three important standards for color gamut of TVs
ITU-R Rec. BT.709 (usually abbreviated as Rec.709) is the standard used today for just about everything you watch at home. Blu-ray and HDTV content is mastered for this standard, and an HDTV can be expected to display all the colors of Rec.709. However, if you look at Rec.709 in relation to the full CIE1931 color range, you will immediately notice that the triangle comprises only a small part of all colors, namely about 34%. So there is still a lot of room for improvement. The most vibrant, intense colors are right on the edge of the horseshoe shape, so a wider color range (in other words, a larger triangle closer to the edge of the horseshoe shape) will contain more intense colors.
And such standards already exist. DCI-P3 (Digital Cinema Initiative) is used in almost all movie theaters. A film that you watch in the cinemas therefore uses a richer color palette than the same film on Blu-ray. DCI-P3 uses the same blue, but red and especially green are clearly more intense. DCI-P3 contains approximately 46% of all colors.
ITU-R Rec. BT.2020 (short: Rec.2020) is an even larger color range that is used as standard for Ultra HD TV. It has also become the standard for Ultra HD Blu-ray discs. Rec.2020 uses an even stronger green and red, and also a more intense blue to a lesser extent. The range is about twice that of Rec.709 and covers 63% of all colors, which is almost the maximum possible with just three base colors.
Where are the current televisions located?
The Rec.709 color gamut has been rendered almost perfectly by most manufacturers for some time now. But for several years now we have regularly seen screens that advertise a wider color range (or ‘Wide Color’). And since 2015, TV makers are really taking part in Wide Color. This is mainly due to the rise of Ultra HD . We all know Ultra HD as an improvement in the resolution of our televisions. But also an expanded color range and High Dynamic Range display are part of the improvements we can expect from Ultra HD. Although all these improvements can exist strictly independently of each other, in practice you will find a wider color range especially on HDR-compatible televisions.
An important point is that manufacturers do not switch from one standard to another in one step. Reproduction of Rec.2020 or even DCI-P3 is not yet possible. New image technologies such as quantum dots , OLED , or wide color LEDs are required to generate those very intense and pure basic colors.
In the specifications, and in reviews, you will therefore often see references to the percentage of the DCI-P3 or Rec.2020 color range that they can display. The best televisions get about 95% of DCI-P3, or about 70% of Rec. 2020. To really speak of a wider color range, we set the bar on 90% DCI-P3 display, a limit that is also imposed by the Ultra HD Alliance if a manufacturer wants to use the Ultra HD Premium logo .
How does it look?
The impact of a wider color gamut is quite easily visible. Especially if you view images with a lot of red or green. We have simulated the result on the image below from The Martian (bottom image). You may be tempted to use that extensive palette with its rich colors on all your images, but that will not always turn out to be a good choice.
The importance of color scaling
In ideal circumstances, both the content and the display use the same color gamut. After all, this guarantees that you as a viewer see exactly what the director had in mind. Unfortunately, we are currently in a transition phase. All of our content is mastered for home use in Rec. 709. However, modern televisions can display more colors.
So with the current content, manufacturers have two choices. Or they limit the color range of their device. This is usually done if you choose the image preset ‘film’, so that you can be sure of the correct display in that image preset. In other words, they ‘scale’ the color range of the content so that you can enjoy their richer color range. However, the latter option requires a great deal of expertise. Mapping colors on a larger color range without further adjustment often leads to unnatural, bright tones, especially for skin tones.
But if we use recent Ultra HD content mastered in Rec. 2020, aren’t we rid of those problems? No, even then the ‘color scaling’ process is important. Most televisions are not fully DCI-P3 compliant for now, and reaching Rec.2020 could take several more years. Until then, the manufacturer must map the larger color range of the content on the smaller color range of its device. And that also requires quite a bit of expertise.
Purists, who only want to see the director’s original intent, should continue to watch their existing content in Rec.709 (select the ‘Movie’ or ‘Cinema’ image preset on your television). With recent HDR content such as available via Netflix, Amazon or UItra HD Blu-ray, you can enjoy the larger color range. The television itself detects that it is HDR content and then activates the large color range.
Conclusion
A wider color range will eventually lead to very realistic images. With HDR content, the only content that really uses a larger color range, you can already see the effect. But for the very best results, we have to wait until both content and display meet the Rec.2020 standard. Until then, the color scaling performance of recent televisions will have a significant impact on what you get to see.
