Display Color Gamuts Shoot-Out

NTSC to Rec.2020

 

Dr. Raymond M. Soneira

President, DisplayMate Technologies Corporation

 

Copyright © 1990-2016 by DisplayMate Technologies Corporation. All Rights Reserved.

This article, or any part thereof, may not be copied, reproduced, mirrored, distributed or incorporated

into any other work without the prior written permission of DisplayMate Technologies Corporation

 

 

 

Introduction

The Color Gamut defines the range of colors that a display can produce – so it is the most important defining visual characteristic of any display. While Color Gamuts have changed over the years, in the past virtually all displays needed just a single Gamut to produce all of the content that a user wanted to see. But with the recent development of several new larger Color Gamut standards for producing new content, including DCI-P3 for 4K Ultra HD TVs and Digital Cinema, all future TVs, Monitors, Smartphones, Tablets and Laptops will need to support at least two Color Gamuts. We’ll explain how that’s done with Color Management.

 

So there is a big learning curve for consumers, reviewers, content producers, and even manufacturers on the proper use of the new Color Gamuts. In this article we will examine and compare some of the most important Display Color Gamuts that have been appearing in consumer products over the last 60+ years, from the earliest NTSC Gamut up through the latest DCI-P3 and Rec.2020 Gamuts. The Gamuts have been evolving and getting progressively larger...

 

Display Color Gamuts and Standards

Over the years there have been an incredibly wide range of Color Gamuts that have been implemented on displays. Many are simply based on the particular native primary colors conveniently available at the time at low cost for different display technologies like CRT, Plasma, LCD, OLED, LED, Quantum Dots, phosphors, lasers, etc. Many applications just need any suitable range of colors to satisfy a user’s needs. However, essentially all imaging based applications need a specific well defined Color Gamut in order to accurately reproduce the colors in the image content. Over the years this has given rise to many different standard Color Gamuts for the current image content, and they have generally been based on what the currently existing displays at the time could produce. So both the displays and content have evolved together over time, and many different Color Gamuts have been defined, but they are not all created equal...

 

What makes a Color Gamut important and a true Standard is the existence of lots of content created specifically for that Gamut so manufacturers then need to include that Standard in their products. So it is the content and content producers that define a true Color Gamut Standard – the displays then need to deliver it as accurately as possible on-screen. Every display needs to adapt its native Color Gamut for the content that it has to show. This is implemented using Color Management, which we discuss below.

 

While people primarily think of Color Gamuts in terms of their outermost saturated colors, most image content is generally found in the interior regions of the Gamut, so it is particularly important that all of the interior less saturated colors within the Gamut be accurately reproduced.

 

And if you are not sure of the set of colors that the different Gamuts actually produce, we will show you accurately Colorized versions of the two most important Standard Gamuts being used today so you can evaluate them visually. In case you think you have already seen Colorized Gamuts before, the colors shown in essentially all published Color Gamuts are fictitious and wildly incorrect. We have accurately calculated them here.

 

Color Gamuts and Ambient Light

One very important point that applies to all displays is the Color Gamut that you actually see on-screen is reduced by any existing ambient light falling on the screen. Since very few users watch their displays in absolute darkness (0 lux) the visible Color Gamut that is actually seen is noticeably less than 100 percent. We examine this very important effect and its solution in our 2014 Innovative Displays and Display Technology article.

 

NTSC Color Gamut

The first official Color Gamut Standard for displays was the NTSC Color Gamut, which made its debut in 1953 for the beginning of US color television broadcasting. But the NTSC primary colors were too saturated and couldn’t be made bright enough for use in the consumer (CRT) TVs of that era, so the NTSC Color Gamut was Never actually used for volume commercial production of color TVs. As a result, the NTSC Gamut was Never really an actual Standard Color Gamut, and there is essentially no consumer content based on the true NTSC Color Gamut. Which is amusing (and annoying) because now more than 60 years later many manufacturers and reviewers are still quoting and referring to the NTSC Gamut as if it were some sort of state-of-the-art standard, when it has been obsolete and colorimetrically disjoint from most other standard Gamuts for an incredibly long time – we’ll demonstrate why below.

 

Manufacturers of high-tech products should be embarrassed for publishing their specifications in terms of NTSC, an obsolete 60+ year old technology! So please everyone, let’s stop referring to the very outdated NTSC and instead move on to the actual Color Gamuts that are being used in today’s displays. But before we bury it, we’re going to show you what the NTSC Color Gamut looks like in Figure 3 below together with many of the current Color Gamuts, which we’ll cover in turn below...

 

The Real Analog TV and Standard Definition TV Color Gamuts

Instead of the official NTSC Gamut colors, the practical phosphor colors that were actually used in early color TVs were developed by the Conrac Corporation, which eventually became the SMPTE-C Color Gamut Standard. TV production studios used Conrac color monitors to produce their broadcast TV content, so it was the Conrac Color Gamut rather than the NTSC Gamut that was the real color television Standard Gamut. The SMPTE-C Gamut is not that different from today’s sRGB / Rec.709 Gamut, which is 13 percent larger than SMPTE-C. Many later Gamut standards were based on SMPTE-C, including up to Rec.601 for Digital Standard Definition TV. We are now going to skip over lots of history and get to the Display Color Gamuts that are in use today...

 

sRGB / Rec.709 Color Gamut

For over 10 years the main Color Gamut that has been used for producing virtually all Current consumer content for digital cameras, HD TVs, the internet, and computers, including photos, videos, and movies is a dual standard called sRGB / Rec.709. If you want to see accurate colors for this content on just about any consumer product, then the display needs to match the sRGB / Rec.709 Standard Color Gamut – not larger and not smaller, because the colors will then appear wrong and also be either too saturated or under-saturated.

 

There are still widely held beliefs by lots of reviewers and consumers that viewing content on a display with a larger Color Gamut is actually better, but it is definitely worse because the display cannot produce colors that are not present in the original content, so the colors are just shown distorted and over-saturated. We include the Standard sRGB / Rec.709 Gamut in Figures 3 to 6.

 

Below we’ll show you both visually and quantitatively what the sRGB / Rec.709 Color Gamut looks like in both the 1976 and 1931 CIE Diagrams.

 

Accurately Matching the Color Gamut Standard

For reasons similar to what occurred long ago with the NTSC Gamut, up until recently a reasonable fraction of all displays could not produce 100 percent of the sRGB / Rec.709 Color Gamut, particularly for mobile displays, which in many cases provided less than 70 percent of the sRGB / Rec.709 Gamut because of similar brightness and efficiency issues that had plagued the NTSC Gamut. As a result, their on-screen images appeared somewhat bland and under-saturated. But today most good quality products have displays that produce close to 100 percent of the sRGB / Rec.709 Color Gamut.

 

And similar issues also apply to the newest and largest Color Gamuts, DCI-P3 and Rec.2020, which we examine in detail below. 4K UHD TVs only need to provide 90 percent of the DCI-P3 Color Gamut Standard to receive a 4K UHD Alliance certification, and the currently available Rec.2020 displays typically only provide 90 percent of the Rec.2020 Color Gamut Standard. So it has always taken some time for displays to fully and properly implement the latest Color Gamut Standards. However, that introduces color errors that reduce the Absolute Color Accuracy of the displayed content, which we discuss below.

 

Adobe RGB Color Gamut

Most high-end digital cameras have an option to use the Standard Adobe RGB Color Gamut, which is 17 percent larger than the Standard sRGB / Rec.709 Color Gamut that is used in consumer cameras. The Adobe RGB Gamut is also used in many other advanced and professional imaging applications. It has a more saturated Green Primary than the sRGB / Rec.709, which accounts for all of its larger Gamut size. For consumers, Samsung’s Galaxy Smartphone and Galaxy Tablet OLED displays accurately produce the Adobe RGB Gamut as covered in our Mobile Display Technology Shoot-Out article series. We include the Adobe RGB Gamut in Figure 3 below.

 

DCI-P3 Color Gamut

The newest Standard Color Gamut that has significant content is DCI-P3, which is 26 percent larger than the sRGB / Rec.709 Gamut. It is being used in 4K Ultra HD TVs and in Digital Cinema for the movie industry, so while the amount of existing DCI-P3 content is still relatively small compared to sRGB / Rec.709, it is now starting to grow rapidly. DCI-P3 is also being adopted in many other new displays and applications that want to provide a larger Color Gamut with a wider range of more saturated colors. We recently tested the new Apple iPad Pro 9.7, which has a very accurate native 100% DCI-P3 Gamut, and it also produces a very accurate 100% sRGB / Rec.709 Gamut by using Color Management, which we discuss below. We include the Standard DCI-P3 Gamut in Figures 3 and 6.

 

Color Spectra

Displays (and everything in nature) all produce their color by controlling and varying the amount of energy from different wavelengths of light. The color sensations that we all see are produced entirely within the brain from electrical signals produced by the eye from the wavelength distributions of light it receives. The CIE Color Diagrams that we show below relate the wavelength distributions to the colors that we see. So a good way to compare Display Color Gamuts is by first examining their light spectra.

 

To see how different the DCI-P3 Color Gamut is from sRGB / Rec.709, Figure 1 below compares the white light spectrum of an Apple iPad Pro 9.7 that has a native DCI-P3 Gamut, with an Apple iPad Air 2 that has a native sRGB / Rec.709 Gamut. Note how much narrower and more widely spaced the DCI-P3 Primary Colors are, which results in more saturated Reds and Greens. We include the DCI-P3 Gamut in Figures 3 and 6 below.

 

Figure 1.  Spectrum Comparing DCI-P3 and sRGB / Rec.709 Gamuts

 

 

Rec.2020 Color Gamut

The next generation Standard Color Gamut will be the impressively large Rec.2020 standard, shown in Figures 2 and 3 below. In fact, it is 72 percent larger than sRGB / Rec.709 and 37 percent larger than DCI-P3. The Color Gamut is extremely wide and the Color Saturation extremely high. However, there is almost no current existing content for Rec.2020. And there are very few existing displays that come close to providing Rec.2020, which requires Quantum Dots for LCDs. Of course, continuing progress is being made in extending the Color Gamuts for both LCD and OLED displays, so Rec.2020 will become an important new Standard Gamut within the next several years.

 

To see how incredibly challenging Rec.2020 is, Figure 2 below compares the white light spectrum of a Vizio R65 TV (courtesy of Nanosys, which makes the Quantum Dots) that has about 90 percent of the Rec.2020 Gamut, with an Apple iPad Pro 12.9 that has a native sRGB / Rec.709 Gamut. Note how narrow and widely spaced the Rec.2020 Primary Colors are, and how far the Red Primary is. resulting in significantly more saturated colors. We include the Rec.2020 Gamut in Figure 3 below.

 

Figure 2.  Spectrum Comparing Rec.2020 and sRGB / Rec.709

 

 

Comparing the Standard Color Gamuts

Figure 3 below shows the Color Gamuts for most of the Standards that we have been discussing. They are all plotted on a CIE 1976 Uniform Chromaticity (Color) Diagram that quantitatively evaluates color in a perceptually uniform manner for human color vision with (u’,v’) color coordinates. All of the color regions and visual differences between colors remain consistent throughout the entire 1976 CIE Color Space, so it provides an excellent and accurate method for specifying, manufacturing, marketing, comparing, measuring, and calibrating displays.

 

Note that the older 1931 CIE Diagrams, with (x,y) color coordinates, that are published by many manufacturers and reviewers are very non-uniform and distorted, so they are effectively meaningless for quantitatively evaluating Color Gamuts and their Color Accuracy. The Color Gamuts shown in Figure 4 would appear very different in the 1931 CIE Diagram. We’ll examine this in detail for the sRGB / Rec.709 Gamut below.

 

To get a better understanding for what the Color Gamuts actually produce we’ll show you below accurately Colorized versions of the two most important Gamuts being used today.

 

In all of the CIE Diagram Figures below, the outermost white curve is the limits of human color vision – the horseshoe is the pure spectral colors and the diagonal is the Line of Purples connecting Red and Blue at the extreme ends of human color vision. Green is between Red and Blue in the spectrum, and is on the extreme left in the CIE Diagrams. The Colorized Gamuts in Figures 4 to 6 below will show this visually for one Color Gamut at a time.

 

A given display can only reproduce the colors that lie inside of the triangle formed by its three Primary Colors, which are always based on Red, Green, and Blue, following the eye’s own spectral color response. The larger the Color Gamut the greater the range of colors that can be produced. Some displays have more than three primary colors. In such cases the Color Gamut is then defined by a polygon. Sharp’s Quattron for example, includes a fourth Yellow (non-standard) primary that actually improves the display’s brightness and efficiency more than enlarging the Gamut as seen from Figure 3.

 

When content is being produced, colors that are outside of the content’s Color Gamut move automatically to the closest available color and no longer exist and cannot be recovered later by using a larger Color Gamut. So the highly saturated colors outside of the Color Gamut are still reproduced but with lower color saturation.

 

Standard Color of White

The Standard Color of White for almost all current Color Gamut standards is called D65, which is the color of outdoor natural Daylight at noon with a Color Temperature close to 6500K, is marked in the Figures below as a white circle near the middle. To deliver accurate image colors a display must match the same Color Gamut and also the same Color of White that was used to create the content. Unfortunately, many displays accurately reproduce the Color Gamut, but then use an inaccurate (typically too blue) White Point, which then introduces color accuracy errors throughout the entire inner regions of the Color Gamut.

 

Color Gamut Size Comparisons in Terms of Area

A common metric for comparing the relative sizes of the Color Gamuts is by using their relative areas within the Uniform 1976 CIE Diagram. The relative Gamut sizes that are calculated from the non-uniform 1931 CIE Diagram are significantly different and are compared in a later section below.

 

The Adobe RGB Color Gamut is 17 percent larger than sRGB / Rec.709.

The DCI-P3 Color Gamut is 26 percent larger than sRGB / Rec.709.

The Rec.2020 Color Gamut is 72 percent larger than sRGB / Rec.709 and 37 percent larger than DCI-P3.

 

And for those of you still interested in NTSC Gamut statistics:

The NTSC Color Gamut is 98 percent of the Adobe RGB Color Gamut. So while they are both very close in Gamut area and size, note how very different their triangular Gamut shapes and color regions are in Figure 3, proving that the still current practice of using NTSC for Gamut specifications and comparisons has little colorimetric meaning or useful quantitative value for the current Gamuts and displays (and doubly wrong when combined with the non-uniform 1931 CIE Color Space).

 

Color Gamut Comparisons in Terms of Just Noticeable Color Differences JNCD

A better metric for evaluating the new larger Color Gamuts is by how different their Primary Colors are in terms of visual Just Noticeable Color Differences JNCD from the Standard sRGB / Rec.709 Primary Colors, calculated using the Uniform 1976 CIE Diagram, where visual color differences are proportional to the linear distances between any two colors in the Diagram. Figure 4 shows the distances corresponding to 1 JNCD and 3 JNCD, with 1 JNCD = 0.0040 in the (u’,v’) 1976 Uniform Color Space. The 1931 CIE Color Space cannot be used for JNCD because it is Non-Uniform.

 

For Adobe RGB the Green Primary is 12.8 JNCD from sRGB / Rec.709.

For DCI-P3 the Red Primary is 11.4 JNCD and the Green Primary is 7.6 JNCD from sRGB / Rec.709.

For Rec.2020 the Red Primary is 26.5 JNCD, the Green Primary is 18.4 JNCD, and the Blue Primary is 9.0 JNCD from sRGB / Rec.709.

 

So the Visual Color Differences between the Color Gamuts are quite large, very noticeable, and significant.

 

Figure 3.  Standard Color Gamuts Plotted on a CIE 1976 Uniform Chromaticity Diagram

 

Next we’ll examine accurately Colorized versions of the sRGB / Rec.709 and DCI-P3 Color Gamuts to visually examine and quantitatively compare their Color Spaces.

 

Accurately Colorized sRGB / Rec.709 Color Gamut

Figures 4 and 5 below show an accurately Colorized sRGB / Rec.709 Color Gamut. For displays this can only be done for a single Color Gamut at a time. The colors in the Figure have been accurately calculated to show the real colors within the sRGB / Rec.709 Gamut – the colors shown in most published Color Gamuts are fictitious and wildly incorrect. Also included are 41 Reference Colors that we use for measuring the Absolute Color Accuracy throughout the entire Gamut, which is discussed below.

 

Note that printed versions of the Colorized Gamuts depend on the particular inks being used and also their spectral absorption of the particular ambient light you are viewing them in, so they cannot be as accurate as an emissive display, and they also generally provide smaller Gamuts than most displays.

 

In order to see the actual accurate colors in the Colorized Gamut, your display must be set to the sRGB / Rec.709 Standard (that is found on most recent Smartphones, Tablets, Laptops, Monitors, and Full HD TVs for example) or support active Color Management. Otherwise, the colors will be incorrect, and much too saturated if you are watching on a DCI-P3 UHD TV or display as discussed below.

 

Note that every color within the Gamut is shown at its maximum Brightness (Luminance). White is the brightest color near the middle because it is the sum of the Peak Red, Green, and Blue Primary Colors. The Secondary Colors of Cyan, Magenta, and Yellow radiate from the White Point as ridges because they are the sums of two Primary Colors.

 

One particularly interesting result seen in Figure 4 is how relatively small the Green region of the sRGB / Rec.709 Color Gamut is in the accurate 1976 CIE Uniform Color Space, accounting for just 10 percent of the total Gamut. However, the Green region is rendered 2.4 times larger in the distorted and Non-Uniform 1931 CIE Chromaticity Diagram, as shown in Figure 5 below. The newer Color Gamuts: Adobe RGB, DCI-P3, and Rec.2020 all significantly enlarge the Green region of their Color Space within the Uniform 1976 CIE Diagram.

 

Figure 4.  Accurately Colorized sRGB / Rec.709 Color Gamut with Reference Colors

 

Absolute Color Accuracy and Just Noticeable Color Differences JNCD

One very important issue is the accuracy of each display’s Color Gamuts, and the Absolute Color Accuracy for all of the colors within the entire Color Gamut. One very important reason for accurately Colorizing and rendering each Color Gamut in the 1976 CIE Uniform Color Space is that the display’s Color Accuracy and Color Calibration can be accurately analyzed uniformly, and then the true Color Errors uniformly minimized for all of the colors within the Color Gamut. The errors are expressed in terms of Just Noticeable Color Differences JNCD, which correspond to fixed linear distances within the CIE Diagram. Figure 4 shows the distances corresponding to 1 JNCD and 3 JNCD, with 1 JNCD = 0.0040 in the (u’,v’) 1976 CIE Color Space.

 

For each tested display we measure the Absolute Color Accuracy of 41 Reference Colors, which are shown for sRGB / Rec.709 in Figure 4. For a good example, see this color accuracy analysis for both the DCI-P3 and sRGB / Rec.709 Color Gamuts in the Apple iPad Pro 9.7, which includes a more detailed discussion of JNCD.

 

In our Display Absolute Color Accuracy Shoot-Out article we show the colors for a wide range of facial skin tones and fruits and vegetables so that you can get a good idea of where these important colors fall within the 1976 CIE Diagram.

 

Accurately Colorized 1931 CIE Diagram for the sRGB / Rec.709 Color Gamut

The best way to demonstrate the large differences between the 1976 Uniform and the older 1931 Non-Uniform CIE Diagrams is to show an accurate Colorized sRGB / Rec.709 Color Gamut for both of them side-by-side in Figure 5. Note that for the comparison both of the Color Triangles have been scaled to have the same geometric area in the Figures.

 

Note how differently the colors are distributed within each Color Space. The obsolete but still widely used 1931 CIE Diagram has a very non-uniform Color Space that significantly expands the Green region (by a large factor of 2.4 in area) and significantly compresses the Blue Region (by a large factor of 1.7 in area), providing a very distorted representation of human color perception. The Red regions are only 7 percent different in area, but note how different their shapes are.

 

Specifying and analyzing displays in terms of the very non-uniform and very distorted 1931 CIE Color Space introduces significant performance, calibration and color accuracy errors. Many manufacturers also specify their guaranteed display color accuracy in terms of the non-uniform (x,y) 1931 CIE coordinates, which results in large variations and differences in color accuracy throughout the Color Space.

 

The 1976 CIE Diagram transforms and corrects the distortions in the original 1931 version to produce a Uniform Color Space that accurately renders human color perception and color accuracy. It's about time that manufacturers and reviewers abandon the obsolete 1931 CIE Color Space for all of the above reasons!

 

Figure 5.  Accurately Colorized Comparisons of the 1976 and 1931 CIE Color Spaces

 

Inaccurate Color Gamut Comparisons in terms of the 1931 CIE Diagram:

Note that the relative differences between the Color Gamuts that we show above are based on the 1976 CIE Uniform Chromaticity Diagram. Some manufacturers and reviewers still specify their Color Gamuts by using the highly non-uniform 1931 CIE Diagram that greatly exaggerates and stretches the relative differences between the Color Gamuts, so those comparisons are very inaccurate and essentially meaningless.

 

The Color Gamut size comparisons that are calculated and specified by many manufacturers using the 1931 CIE Diagram are also very inaccurate and very misleading. For example, in the non-uniform 1931 CIE Color Space the Adobe RGB Color Gamut is 35 percent larger than sRGB / Rec.709, more than double the accurate 17 percent value listed above from the 1976 CIE Uniform Color Space. And in the 1931 CIE Color Space the DCI-P3 Color Gamut is 36 percent larger than sRGB / Rec.709, a 38 percent size exaggeration compared to the accurate 1976 CIE value of 26 percent larger.

 

These large discrepancies prove that using the 1931 CIE Color Space for specifications and comparisons has little colorimetric meaning or useful quantitative value for current displays. Manufacturers should be embarrassed for specifying their products in terms of the obsolete and very misleading non-uniform 1931 Color Space!

 

Accurately Colorized DCI-P3 Color Gamut

Figure 6 below shows an accurately Colorized DCI-P3 Color Gamut. For displays this can only be done for a single Color Gamut at a time. The colors in the Figure have been accurately calculated to show the real colors within the DCI-P3 Gamut – the colors shown in most published Color Gamuts are fictitious and wildly incorrect.

 

In order to see the actual accurate colors in the Colorized Gamut, your display must be set to the DCI-P3 Standard (on a 4K UHD TV or Apple iPad Pro 9.7 for example) or support active Color Management. Otherwise the colors that you see will be incorrect. They will all appear significantly under-saturated if you are watching on a sRGB / Rec.709 display as discussed above.

 

Note that every color within the Gamut is shown at its maximum Brightness (Luminance). White is the brightest color near the middle because it is the sum of the Peak Red, Green, and Blue Primary Colors. The Secondary Colors of Cyan, Magenta, and Yellow radiate from the White Point as ridges because they are the sums of two Primary Colors.

 

Figure 6.  Accurately Colorized DCI-P3 Color Gamut

 

 

Differences Between the DCI-P3 and sRGB / Rec.709 Gamuts

Figure 7 below shows an accurately Colorized DCI-P3 Color Gamut with an inscribed sRGB / Rec.709 Gamut in order to show the differences between the two Gamuts.

 

If your display is set to DCI-P3 then the colors both inside and outside of the sRGB / Rec.709 triangle will be accurate, so you can see what the new set of more saturated colors in the DCI-P3 Gamut provide. If your display is set to sRGB / Rec.709 then the colors will all appear as less saturated sRGB / Rec.709 Gamut colors, however, you will still get an idea of how much larger the DCI-P3 Color Gamut actually is.

 

Important New Saturated Green and Red Color Regions

Note how much larger the Green region in the DCI-P3 color space is in comparison to sRGB / Rec.709, by 52 percent. The extreme Reds have also been significantly expanded. Based on the measurements in our Absolute Color Accuracy Shoot-Out, most fruits and vegetables are found in the most saturated Red to Orange to Yellow to Green regions of the Color Space (so they visually attract animal attention for eating and spreading their seeds), and the most highly saturated colors are also heavily utilized in lots of human generated content in order to get people’s visual attention, so the enlarged Red to Green sliver in the DCI-P3 Color Space is actually very important.

 

Figure 7.  Comparing the sRGB / Rec.709 and DCI-P3 Color Gamuts

 

 

An Accurately Colorized Rec.2020 Color Gamut

It is still premature for us to generate an accurate Colorized Rec.2020 Color Gamut at this time because there are currently very few displays that come close to providing Rec.2020, and there is almost no current existing content for Rec.2020. As a result, a Colorized Rec.2020 Color Gamut would appear just like the smaller native Color Gamut of your current display. And printed inks are also unable to reproduce the highly saturated Rec.2020 colors.

 

When things advance a bit further, we’ll revisit the entire topic of Display Color Gamuts...

 

Color Management for Multiple Color Gamuts

When a display needs to support one or more additional Color Gamuts like sRGB / Rec.709 that are smaller than its native Color Gamut, that can be accomplished with digital Color Management performed by the firmware, CPU or GPU for the display. The digital R,G,B values for each pixel in an image being displayed are first mathematically transformed so they colorimetrically move to the appropriate lower saturation colors closer to the White Point. The available Color Gamuts can either be selected manually by the user, or automatically switched if the content being displayed has an internal Tag that specifies its native Color Gamut, and that Tag is recognized by the display’s Operating System or firmware. The Apple iPad Pro 9.7 implements Color Management that automatically switches between the DCI-P3 and sRGB / Rec.709 Gamuts.

 

Another more advanced color management approach is for the content to include meta-data with detailed specifications for the colorimetry of the content, and then it is up to the display to implement it as accurately as possible using its native Color Gamut colorimetry and photometry.

 

Summary and Conclusion

Our overview of Color Gamuts from the earliest NTSC Gamut to the latest DCI-P3 and Rec.2020 Gamuts has demonstrated the importance of eliminating the widespread use of the obsolete 1953 NTSC Gamut and the obsolete 1931 CIE Diagram in the display industry. Switching to current display technology standards is now tremendously overdue.

 

The 1953 NTSC Gamut was never actually used for production displays, and is colorimetrically different from current standard Gamuts, so it is misleading to use as a Reference Gamut. The 1976 CIE Diagram transforms and corrects the large distortions in the original 1931 Diagram to produce a uniform color space that accurately renders human color perception and color accuracy.

 

Switching to current colorimetry standards is not only essential for properly specifying, measuring, manufacturing and accurately calibrating displays, but also for comparing and marketing them to both product manufacturers and consumers.

 

 

About the Author

Dr. Raymond Soneira is President of DisplayMate Technologies Corporation of Amherst, New Hampshire, which produces display calibration, evaluation, and diagnostic products for consumers, technicians, and manufacturers. See www.displaymate.com. He is a research scientist with a career that spans physics, computer science, and television system design. Dr. Soneira obtained his Ph.D. in Theoretical Physics from Princeton University, spent 5 years as a Long-Term Member of the world famous Institute for Advanced Study in Princeton, another 5 years as a Principal Investigator in the Computer Systems Research Laboratory at AT&T Bell Laboratories, and has also designed, tested, and installed color television broadcast equipment for the CBS Television Network Engineering and Development Department. He has authored over 35 research articles in scientific journals in physics and computer science, including Scientific American. If you have any comments or questions about the article, you can contact him at dtso.info@displaymate.com.

 

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Article Links:  Display Absolute Color Accuracy Shoot-Out

Article Links:  Mobile Display Shoot-Out Article Series Overview and Home Page

Article Links:  TV Display Technology Shoot-Out Article Series Overview and Home Page

 

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