Representing color on screens is a complex process; But if you are looking for quality images, it is worth a look. If you look closely at the TVs next to each other in the electronics store, you may notice some differences. If you display the same image on all of them, the color outputs will be different.
What is a colored gamut?
In general, the term gamut refers to all the colors that the eye can see. The gamut is usually represented by a horseshoe shape called the xy chromaticity chart. There is also a 3D display for it. However, in the computer graphics industry, the gamut demonstrates the display color adjustment capabilities. Simply put, it is a scale of colors that any monitor can produce.
Color gamutes represent a subset of the xy chromatochemical diagram, which is always represented as a triangle. In other words, monitors can display part of the entire visible color. sRGB is the most common display color gamut shown in the diagram below. The sRGB display cannot produce any color outside the triangle.
The larger part of the triangle means that the display gamut covers a larger percentage of the visible spectrum. The greater the overlap between the color gamut of the display and the resolution of the eye, the better the output. None of the current monitors on the market can cover the entire visible spectrum; But this is not a problem.
Bit depth
Before we talk about the different types of color gamut, it’s best to get an idea of how color is produced in monitors. In general, monitors are made up of blue, red, and green sub-pixels that combine to produce the desired color. These sub-pixels are not visible to the naked eye; But you can see them under a microscope.
A wide color gamut is not the only criterion for a good image to look good. Also, monitors should be able to produce unique shades of red, green, and blue within their color gamut. Bit depth can be used to measure the number of unique shades that can be produced for the display. Simply put, the bit depth is equal to the amount of data used to display the brightness level of each subpixel. An 8-bit display creates 2 to 8 or 256 shades of each primary color (blue, red, and green). In total, 16.7 million vessels are produced. A 10-bit display can also produce 1024 shades or a total of 1.07 billion colors.
Bit depth further ensures that the display can create precise transitions or gradients between colors. This is especially important for wide gamut monitors. You can see the bit depth display in the image above. Today, there are more specialized definitions of color gametes, some examples of which are given below.
sRGB
sRGB or RGB standard is the oldest and most common color space today. In the 1990s, the International Electrotechnical Commission (IEC) designed this gamut for CRT monitors. It has since adapted to LCDs and other display technologies.
Although sRGB is very popular, it covers only part of the visible light spectrum. Simply put, a simple sRGB display can reproduce 25 to 33% of the colors that are recognizable to the eye. Examining the chromaticity diagram, you can see that many of the outer areas of the main colors are not in this space.
Although sRGB includes a range of red, green, and blue colors, it does not cover the more saturated areas. This is especially felt when examining green areas; For this reason, the brightness and vibrancy of the color decreases and the colors may appear more opaque than they are.
sRGB is closely related to Gamut Rec. Has 709. In fact, the two standards cover the same area of the chromaticity chart, with the only difference being that sRGB uses less gamma than Rec.709. Lower sRGB gamma improves color perception in bright rooms such as office spaces.
Rec.709 is designed for TVs and monitors in light spaces. Because most displays allow you to adjust the gamma value, the difference between sRGB and Rec.709 is negligible. sRGB has become the predominant standard for displays of all shapes and sizes, despite the limited color coverage. Most PC operating systems, including Windows, are configured for sRGB. Similarly, most websites and their content are sRGB compliant.
AdobeRGB; Suitable for pictures
AdobeRGB, as its name implies, is a color space developed and popularized by Adobe. This space is wider than sRGB and covers approximately 50% of the visible color spectrum. AdobeRGB, unlike most other color spaces, is not used for video; Rather, it is specifically designed for photography. To understand this, consider color printers.
You may have noticed that printers do not combine blue, red, or green (RGB) ink to produce color prints; Rather, most color printing equipment uses the CMYK color model (abbreviated as turquoise, purple, yellow, and black). In 1998, Adobe expanded the AdobeRGB space to cover this color space so that photographers could have more control over their print images. AdobeRGB also includes a limited sRGB coverage of cyan and green colors, which you can see by looking at the chromaticity chart.
While AdobeRGB is undoubtedly a great space for photography, most cameras use sRGB color space by default. This is because most of the images on the screens are displayed digitally. In addition, even on compatible displays, most applications cannot output AdobeRGB. For example, if a website contains an AdobeRGB file, web browsers will automatically display it as sRGB compliant. However, this conversion process is not perfect, and often the result will look worse than the sRGB image.
In short, setting up AdobeRGB content requires the use of image-specific tools and software. If a file is improperly configured, you may encounter a low quality sRGB image. In addition, the low consumer demand for this space in recent years means that AdobeRGB is not a popular color gamut. However, some monitors have custom image profiles that have been calibrated for this space.
DCI-P3
DCI-P3 stands for Protocol 3 Digital Cinema Action, made by the movie industry as an alternative to sRGB. This space covers 27% of the chromaticity chart area, which is very similar to AdobeRGB. However, despite the green deviation, AdobeRGB turquoise P3 space is distributed in three primary colors. In practice, this means that DCI-P3 displays can display more vivid and saturated colors.
Because the DCI-P3 is designed for use in digital media, it is more flexible than AdobeRGB. Also, almost all types of digital devices, from TVs to smartphones, cover at least part of this color space. In addition, higher quality displays cover up to 90% of this space.
Rec. 2020 And Rec.2100
Rec.2020 and 2100 are the newest gamuts on this list. In addition to covering the largest area of the chromatographic chart, Rec.2020 also helped define the UHDTV (High Definition Television) standard. Simply put, it is the first standard to support 10-bit and 12-bit displays and higher resolutions such as 4K and 8K. It defines a higher refresh rate between 60Hz until the 120Hz Is also included.
Gamut Rec. 2020 will cover about 75% of the visible light spectrum, which is 40% more than the DCI P3, and is even a big step compared to sRGB. In fact, this color gamut is so vast that even the best displays cover only 60 to 80% of it. Advances in micro-LED technology and quantum dot displays lead to improved color production capabilities in the long run.
Rec.2100 is an enhanced version of Rec.2020; But some of its parameters, such as color coverage, have remained the same. Its only advantage is the support for high dynamic range (HDR) through two technologies: Gamma Log Hybrid (HLG) and Perceptual Quantization. The second technology forms the basis of HDR formats such as HDR10 and Dolby Vision, and HLG is used exclusively for television broadcasting.
Beyond colors: color errors and white dots
While the wide color gamut is quite desirable, it is not the only sufficient criterion for the quality of the display. We have already talked about the effect of gamma length and color depth on the received image. In this respect, no two displays are the same; Even if the gametes are almost identical in color. The reason for this is the existence of various criteria that change the color rendering capability of the screen. You will not usually find this feature on most monitors. In addition to color coverage, two other criteria must be considered: Delta E and color temperature.
Delta E
Delta E can be considered as a way to measure errors in the color output of the display; But what is the screen error in practice? For example, suppose the display shows red as dark orange. The Delta E, meanwhile, measures the difference between display color output and standard gamutos such as sRGB. As an example, the chart below shows the One Plus 8 Pro display index versus the sRGB standard. The result shows that the display is well calibrated in most places, except for some yellow and orange parts. Delta E average (Difference between output and reference) in this sample is approximately equal to 2.8.
The value of Delta E below is an indication of an incomprehensible error, at least for the human eye. Experts who use calibrated displays prefer a maximum Delta E of 2.0. Any amount greater than this and the change in color accuracy is clearly recognizable.
Color temperature
The white dot, also known as the color temperature, has a large effect on the appearance of the white colors of the display. For example, the image below shows how each white looks on different screens. Usually, color temperature is measured in Kelvin, and color temperature values are in the range of 4,000 to 7,000 Kelvin; But why do we use Kelvin; While we are not talking about the actual temperature of the screen? Because this scale corresponds to the color of the light emitted from a bright, hot metal object. For example, flame gas is seen in the yellow spectrum and at the other end is the blue spectrum. In monitors, we usually call white with a blue coating a cooler white.
The color standards of the white dot display are 6500 K, also known as the D65. The color temperature of sunlight is between 5,000 and 6,000 Kelvin. If the Delta E values or white dot exceeds a certain limit, it is possible to recalibrate the display. In fact, quality monitors that are properly calibrated from the factory may be distorted in the long run. In addition, calibration tools are not cheap, and only specialists can detect small errors.
Why are wide color gamutes so popular?
Our eyes have become accustomed to the limited sRGB gamut over the past decades; However, this is because until a few years ago, only a handful of monitors were equipped with wider color gamut. The display industry has finally reached the point where today, panels with wide color gamut are readily available to the public. At the same time, advances in camera technology have allowed filmmakers to capture more color detail. The combination of these two advantages has made gamuts such as the DCI-P3 affordable and affordable.
Many flagship and mid-range smartphones also provide good coverage of the DCI-P3 color space Offer. Some flagships, such as the Sony Xperia 1 and iPhone 13, record movies in a wider color gamut. Similarly, televisions and monitors from sRGB has passed. In terms of software, both mobile and desktop operating systems also support more color spaces than sRGB.
The move of the content industry to HDR has helped drive demand in wider color spaces. In fact, you can view most content, from video games to TV shows, in wider gamers than sRGB. For this purpose, HDR resources such as game consoles and video streaming services and even TVs are available in wide color gamut. Even web design standards like CSS have begun to support Display P3 (Apple’s implementation of DCI-P3).
In general, the goal of HDR is to bring images closer to reality. As expected, the display of bright color palettes will help to achieve this goal. Most HDR formats, including Dolby Vision and HDR10 +, require displays and content that cover at least the DCI-P3 color space. The goal of the display industry is to fully cover wider color spaces such as Rec. 2020 is in the near future.
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