Title image from the future Xiaozhi, authorized
This article was written in March 2021, and some examples may be outdated.
Before we start, let's talk about color gamut.
Color Gamut#
According to Wikipedia, color gamut is a method of encoding colors and refers to the total range of colors that a technical system can produce. In computer graphics processing, color gamut is a complete subset of colors. The most common application of color subsets is to accurately represent a given situation, such as a specific color space or the color range of an output device."
In short, color gamut refers to the range of colors that a display can show. It is mainly divided into sRGB, NTSC, and wide color gamut standards such as AdobeRGB and DCI-P3 based on the coverage range compared to the human eye's color range.
sRGB?#
sRGB color space (standard Red Green Blue) is a standard RGB color space developed by Hewlett-Packard and Microsoft in 1996 for displays, printers, and the internet. This standard is supported by W3C, Exif, Intel, Pantone, Corel, and many other industry vendors. Open-source software like GIMP also supports this standard, and it is used in proprietary or open graphics file formats like SVG.
Microsoft led the development of the sRGB standard in 1997. Since Windows has a large user base and supports sRGB in various devices such as PCs, cameras, scanners, printers, and projectors, almost all content on the internet is based on sRGB.
NTSC?#
NTSC (National Television System Committee) is a color television broadcasting standard established by the National Television System Committee in December 1952. The two main branches are NTSC-J (Japanese standard) and NTSC-US (also known as NTSC-U/C, the American and Canadian standard).
It is an interlaced system with 60/1.001 fields per second, 525 scan lines, and a horizontal resolution equivalent to 330. The aspect ratio is 4:3.
The chrominance signal modulation of this standard includes balanced modulation and orthogonal modulation, which solves the compatibility problem between color and black-and-white television broadcasting. However, it has the disadvantage of phase distortion and unstable color. Some people jokingly refer to NTSC as "Never The Same Color" or "Never Twice the Same Color."
NTSC was established by the National Television Standards Committee in 1953 to provide a standard for the newly introduced CRT color television at that time. However, it is too old and no longer suitable for modern displays (Apple DOS 3.1 was released in 1978, and MS-DOS was released in 1980). Moreover, for PCs and mobile devices, there are hardly any content creators who work in the NTSC color space. The most common use of NTSC is for comparison with other color spaces.
However, NTSC is actually a color gamut standard that no one follows. Nevertheless, many unprofessional testing organizations and manufacturers like to use NTSC to indicate their color gamut coverage, even though consumers cannot intuitively understand how the screen performs through this value.
AdobeRGB?#
Adobe RGB color space is a color space developed by Adobe Systems in 1998. The purpose of its development is to utilize the RGB color mode of computer displays and other devices as much as possible in CMYK color printing. Adobe RGB color space roughly includes the visible colors in 50% of the Lab color space, mainly improving the coverage in the cyan-green color range.
Adobe RGB, also known as Adobe RGB 1998, was customized by Adobe and adds CMYK color gamut on top of sRGB. It mainly improves the coverage of cyan-green colors and is widely used in the printing industry. It can cover approximately 50% of the CIE (visible colors to the human eye).
DCI-P3?#
DCI-P3, or DCI/P3, is a wide color gamut standard introduced by the American film industry and is one of the color standards for digital cinema playback devices. DCI stands for Digital Cinema Initiatives and was established in 2002 by several major American film companies, including MGM, Disney, Universal, Warner, 20th Century Fox, and SPE.
DCI-P3 is a color gamut that has been used in digital movies in recent years. In 2017, all digital movies in the United States must cover DCI-P3. However, as early as September 2015, Apple's iMac was the first to adopt the P3 wide color gamut.
WTF???#
If you don't understand the above information (I also don't understand)
Let me summarize it for you.
If a display has a wide color gamut, it means that the cost of backlighting increases, and the price of the display will not be cheap.
So how do we choose?
For PC, Mac, or iOS Android users, the most suitable color gamuts to describe the screen are undoubtedly sRGB and Adobe RGB.
But for TVs or home theaters, the most suitable color gamuts should be DCI-P3 and Rec.2020.
DCI-P3 is a wide color gamut standard used in digital movies in recent years. In 2017, all digital movies in the United States must cover DCI-P3.
REC-709 is the name of the film and television industry for sRGB, which is the color gamut standard used in early color televisions and is still widely used in the film and television industry in China.
Is a higher color gamut coverage better?
Not necessarily.
According to @Navis Li on Zhihu:
If your display covers a color gamut beyond sRGB without calibration, you are likely to see oversaturated or completely incorrect colors. Although the first impression may be vibrant, these colors are not what they should originally be.
If you have a PC that covers more than sRGB (such as 100% Adobe RGB), unless you have printing requirements, it may not be useful to you. And if it is not calibrated, what you see on web pages, videos, images, and games will still be no different from a 100% sRGB screen because the creators of these contents work in sRGB.
The ideal state is to cover exactly 100% sRGB, so for ordinary users, it can be used without calibration (of course, calibration is still required for professional needs). The next best option is a screen with a color gamut coverage of over 85% sRGB.
For ordinary users, the images and videos they see rarely contain uncommon colors, so there is not much difference between 80% sRGB and 100% sRGB. They can still experience similar effects to a 100% sRGB screen.
For 55% to 80% sRGB, exceeding 60% is considered acceptable. If you have never seen a better display, as long as the color accuracy and viewing angle are good, it can still be used. However, unlike the previous range of 80% to 100%, the higher the coverage, the harder it is to perceive the improvement. For example, there is almost no difference between 85% and 95%, but there is a significant difference between 65% and 75%. So in this range, the higher the coverage, the better.
Unfortunately, if a screen can only cover 55% sRGB or less, it is a bit regrettable... unless it is very cheap or the cost of this product is spent elsewhere, otherwise it is a pit.
So now you should know that a higher color gamut coverage is not necessarily better for ordinary users who do not plan to calibrate their displays.
So does a higher color gamut coverage mean more oversaturated colors?
Let's talk about color accuracy.
Color Accuracy#
Color accuracy, also known as ΔE, is a crucial reference value on professional displays. It refers to the difference between the displayed colors and the standard colors. The standard colors can be generated through computer data. Obviously, the smaller the difference (ΔE), the better the color accuracy.
ΔE represents the accuracy of displayed colors. The larger the ΔE, the more severe the color deviation. Generally, it is difficult for the human eye to distinguish differences when the average ΔE is below 3. If it is below 1, it can be considered a highly accurate display.
The goal of ΔE and JNCD is the same, which is to measure the difference in color perception between two colors in human visual perception.
If the average ΔE exceeds 6, it can be easily perceived, and if it is below 3, untrained users cannot directly distinguish the difference.
Summary#
For relatively cheap displays used in daily life and office settings, their color accuracy is generally within the range of ΔE 2.5-3, which is easily achievable. However, for applications such as image processing and film production that require high color accuracy, a ΔE < 1.5 is generally required. If ΔE < 1, then the display device is already very professional.
In general, displays with a ΔE < 3 are acceptable to users, but the application level may vary. Displays with a ΔE > 3 are already unacceptable to the human eye.
Color Balance#
In computer graphics, color balance is a term that represents the dynamic range of colors in an image. In traditional art, painters can choose a color palette to express the emotions of their works. In the field of image processing, color balance often refers to the ability to obtain correct colors on specific display or printing devices by changing the color values of the image.
Another related image processing process is color mapping, which maps the color values of each pixel in the image to the 8-bit 256-color format used by old computer displays and image storage formats. Although the human visual system can distinguish more colors than cameras or photographs, the details in the image can still be simulated using color balance with a color palette. Some methods use histogram equalization to achieve color balance.
Gamma Curve#
The purpose of gamma encoding images is to compensate for the characteristics of human vision, thereby maximizing the use of data bits or bandwidth to represent black and white based on human perception of light or darkness. In typical lighting conditions (neither pitch black nor dazzlingly bright), human vision generally has gamma or power function properties. If images are not gamma-encoded, the utilization of data bits or bandwidth will be uneven—there will be too many data bits or bandwidth used to represent differences that humans cannot perceive, while there will be insufficient data bits or bandwidth to represent the visual perception range that humans are very sensitive to. Gamma encoding of images is not necessary (and sometimes counterproductive), as floating-point color values already provide a linear approximation of the logarithmic curve.
In simple terms, gamma is a curve that determines the relationship between brightness and darkness in an image.
Summary#
In the above text, we have selected color gamut, color accuracy, color balance, and gamma curve from the various parameters of a display for explanation.
- Color Gamut: For web users, the best choices are sRGB and Adobe RGB. For audiovisual players or Mac users, the best choice is DCI-P3.
- Color Accuracy: For ordinary users, a display with an average ΔE within 3 is generally acceptable. For users with high color requirements, a display with an average ΔE below 1 is the best choice.
- Color Temperature: Generally, I would choose 6500K as the standard color temperature. It is not only the color temperature of the midday sun but also the standard D65 light source. It is commonly used as the standard color temperature in the image processing industry, although it may appear yellowish to ordinary people.
Is that all?
Not yet.
In addition to the above parameters, there are other factors that affect the display experience:
- Viewing Angle: If the left and right viewing angles are below 60°, they are easily noticeable by observers. Most respondents find angles above approximately 120° acceptable. The same applies to the up and down viewing angles, with angles below 45° being noticeable and angles above 90° being preferable.
- Brightness: In a dark environment (ambient light level below 150 lux), the screen brightness should not be lower than 80 cd/m2 to avoid discomfort and visual impairment. In outdoor environments with indirect sunlight (ambient light level between 2000 and 2500 lux), the screen brightness should be higher than 300 cd/m2 to clearly see the screen content.
- Pixel Density: After the introduction of Retina screens on iPhones, the need for pixel density varies depending on the distance from the screen. Mobile phones generally require a density of 300 PPI to avoid directly seeing pixels, while laptops require at least 150 PPI to be considered good and 200 PPI or higher to be excellent.
- Contrast Ratio: This is a parameter that has been easily overlooked in recent years. The higher the contrast ratio, the more distinct the black and white contrast, which means text will be clearer and sharper when reading, and the occurrence of excessive brightness in black areas when viewing images or videos will be reduced.
References#
【进阶】当评价一款产品时，我们关注的是什么？（一）我们需要什么样的显示器（屏幕）
【视频】4000 元内显示器选购指南 | 设计 剪辑 调色 4K 色准
If you have more thoughts or if there are any errors in this article, please feel free to discuss in the comments below.