Color Gamut

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Introduction to Color Gamut

1. Color Gamut
（1）Core Concept of Color Gamut
Color gamut refers to the range of colors that a technical system (such as a display or printer) or a color space can represent, record, or reproduce. It defines a "palette" of colors—the larger the gamut, the richer the range of colors that can be displayed, particularly those that are vibrant and highly saturated.

Visualization and Benchmark of Color Gamut:The color gamut is typically represented and compared on the two-dimensional chromaticity diagram CIE 1931 Yxy, which is based on the CIE 1931 XYZ color space established by the International Commission on Illumination in 1931.

This chromaticity diagram encompasses all colors visible to the human eye and is shaped like a horseshoe. Any specific color gamut standard can be represented by a polygon (typically a triangle) within this horseshoe shape (the triangle in the figure above represents the sRGB color gamut). The vertices of the polygon correspond to the red, green, and blue primary colors of that color gamut.

2. Mainstream Color Gamut Standards and Their Key Technical Parameters
Different color gamut standards originate from varying industry needs and technological backgrounds. A color gamut standard not only defines the range of colors but also typically includes key technical parameters such as the white point and gamma value, which collectively determine the final color representation.

2.1 sRGB
(1) Origin and Application: Established in 1996 through a joint effort by Microsoft and Hewlett-Packard (HP), its primary goal was to standardize color representation across CRT monitors, printers, and internet content.
It has since become the most fundamental and universal color standard. Virtually all web content, operating systems, and consumer-grade electronic devices default to using sRGB.

(2) Key Technical Parameters:
White Point:D65 (6504K), which simulates natural daylight at noon in Northern Europe.
Gamma Value:Approximately 2.2. This value was initially chosen to match the inherent response of early CRT monitors and also aligns with the human eye's non-linear perception of brightness.

2.2 Adobe RGB
(1) Origin and Application:Proposed by Adobe Systems in 1998. Its primary purpose was to address the inadequacy of sRGB in representing the color gamut of CMYK printing, offering a significant expansion particularly in the cyan-green region. It is primarily used in professional photography and the printing/publishing industries.

(2) Key Technical Parameters:
White Point:D65 (6500K), consistent with sRGB.
Gamma Value:2.2, the same as sRGB.

2.3 DCI-P3
(1) Origin and Application: Defined by the Digital Cinema Initiatives (DCI) organization of the American film industry, it serves as the color gamut standard for digital cinema projection. In recent years, due to its ability to deliver more vivid and visually impactful colors, it has been widely adopted in the high-end consumer electronics sector (e.g., across Apple Inc.'s product line).

(2) Key Technical Parameters:
White Point: Approximately 6300K, slightly warmer, designed to match the viewing environment of movie theaters.
Gamma Value:2.6. This higher gamma value is intended to compensate for the relatively dark viewing conditions in cinemas, providing deeper blacks and higher contrast.

2.4 Rec. 2020 / BT.2020
(1) Origin and Application: A standard defined by the International Telecommunication Union for Ultra-High-Definition Television, covering 4K/8K resolutions. It defines the widest color gamut to date in the consumer domain and serves as a benchmark for the future development of high-definition content.

(2) Key Technical Parameters:
White Point:D65 (6500K).
Gamma Value:2.6, similar to DCI-P3, suitable for home theater environments.
Color Depth:Supports 10-bit or 12-bit, enabling billions to trillions of colors and effectively eliminating color banding in gradients.

2.5 NTSC
(1) Origin and Application:
Origin:The NTSC standard was established in 1953 by the National Television System Committee in the United States and served as the analog color television broadcast standard.
Current Status: It is no longer the production standard for any modern video or digital content. With the transition of television technology from analog to digital, the NTSC standard has been replaced by other digital standards like ATSC (in the US).
Use in the Display Field: Today, the NTSC color gamut primarily exists as a historical legacy and a comparative benchmark in display marketing. Manufacturers often use "XX% NTSC" to roughly indicate the color range size of a display.

(2) Key Technical Parameters:
White Point: Illuminant C (6774K), a bluish white reference point related to the technical conditions and viewing environments of that era.
Gamma Value: Approximately 2.2.

(3) Important Considerations:
Relationship to sRGB: The area of the 100% NTSC color gamut is approximately equal to 72% of the NTSC gamut. Therefore, when a display claims a gamut of "72% NTSC," it roughly corresponds to 100% sRGB coverage. This is a baseline, indicating that the color capability meets a fundamental level.
Marketing Pitfall:A high "NTSC coverage" percentage (e.g., 94%, 100% NTSC) does not directly correspond to the primary color standards we use daily (such as sRGB or DCI-P3). It only indicates that it is a wide-gamut display. However, to understand the actual color performance, one must check its specific coverage of standards like sRGB, Adobe RGB, or DCI-P3. The NTSC percentage should not be used as the primary or sole indicator for measuring color accuracy.

The following table compares the key characteristics of these five major color gamut standards:

Color Gamut Standard	Origin & Primary Application	White Point (Color Temperature)	Chromaticity Coordinates (White, Red, Green, Blue)	Gamma Value	Brief Description of Key Features
sRGB	Microsoft, HP (1996) / Internet, General Display	D65 (6500K)	White:0.3127,0.3290 Red：0.6400,0.3300 Green：0.3000,0.6000 Blue：0.1500,0.0600	≈2.2	Universal baseline; relatively small color range; widest compatibility.
Adobe RGB	Adobe (1998) / Professional Photography, Printing	D65 (6500K)	White:0.3127,0.3290 Red：0.6400,0.3300 Green：0.2100,0.7100 Blue：0.1500,0.0600	2.2	Expanded cyan-greens; better coverage of printing color ranges.
DCI-P3	Digital Cinema Initiatives / Digital Cinema, High-end Consumer Electronics	≈6300K	White：0.3140,0.3510 Red：0.6800,0.3200 Green：0.2650,0.6900 Blue：0.1500,0.0600	2.6	Visually oriented; wider red/green range; more vivid colors.
Rec. 2020	International Telecommunication Union (ITU) / Ultra-HD TV (4K/8K)	D65 (6500K)	White：0.3127,0.3290 Red：0.7080,0.2920 Green：0.1700,0.7970 Blue：0.1310,0.0460	2.6	Future benchmark; widest color range; currently difficult for most devices to fully achieve.
NTSC	National Television System Committee (1953) / Obsolete Analog TV	C (6774K)	White：0.3100,0.3160 Red：0.6700,0.3300 Green：0.2100,0.7100 Blue：0.1400,0.0800	≈2.2	Historical benchmark, not a content standard. 72% NTSC ≈ 100% sRGB.

The following diagram compares the color gamut coverage of these five major color gamut standards:

3. The Importance of Choosing the Correct Color Gamut
Selecting a color gamut is not simply a matter of "the bigger, the better." The key lies in matching the gamut to the workflow and output medium to achieve the desired result. Incorrect matching can lead to color distortion and inaccuracies, which are the most direct and noticeable problems.

Colors Appear Washed-out, Darker, or Desaturated: When a very vibrant color (e.g., a bright red) from the source (like a computer) falls outside the display's gamut, the monitor cannot reproduce that level of vibrancy. It can only output the closest available color within its own gamut, which typically results in a color that is darker, grayer, and less saturated than the one you see in your editing software. Conversely, mismanagement can also cause colors to appear overly saturated and unnatural.

Hue Shifts: Some colors may not just lose vibrancy but can even appear to shift in hue. For example, a bluish-purple might be displayed as a more cyan-blue.

Loss of Detail: In areas with smooth color transitions (like a sunset sky), a limited gamut may prevent the display from reproducing all the subtle color gradations. This can lead to color banding or posterization, where distinct bands of color are visible instead of a smooth blend, resulting in a significant loss of detail.

2. Color Gamut Range and Color Gamut Coverage of Display Devices
When evaluating and comparing the color capabilities of display devices, "Color Gamut Range" and "Color Gamut Coverage" are two core concepts that must be clearly distinguished. They describe the relationship between a display and a color standard from different perspectives.

2.1 Gamut Volume
Definition: Refers to the total area of colors that a display device itself can reproduce. It is an absolute concept describing the hardware's potential capability.
Analogy: Think of it as the entire palette available to an artist. The size of this palette determines how many different pigments the artist can theoretically use.
Representation Method:
It is typically represented on the CIE 1931 chromaticity diagram by connecting the coordinates of the device's own red, green, and blue primary color points to form a triangle (or other shape), with the area of this shape indicating the volume.
In marketing and specification sheets, it is often described as "Wide Gamut" or compared as a percentage of a standard gamut's area, for example, "Gamut volume reaches 120% of the sRGB standard."

2.2 Key Point:
(1) It describes the "maximum capability."
The value can exceed 100%. When stating a "120% sRGB volume," it means the native color gamut triangle area of the display is 1.2 times the area of the standard sRGB triangle, allowing it to reproduce some colors more vibrant than those defined in the sRGB standard.

(2) Gamut Coverage
Definition: Refers to the proportion of a target color standard's (e.g., sRGB, DCI-P3) gamut that a display device's own color gamut can reproduce. It is a relative concept describing how accurately the device matches the standard.

Analogy: Think of it as how well the paints on an artist's palette match the standard list of paints required to recreate a specific painting (like the "Mona Lisa"). The higher the coverage, the more complete their set of standard paints is, enabling a more accurate reproduction of the painting.

(3) Representation Method:
It is usually expressed directly as a percentage of coverage of a specific standard gamut, for example, "99% sRGB Coverage" or "95% DCI-P3 Coverage."

(4) Key Points:
It describes the "degree of match."
The value can approach 100% infinitely but cannot exceed it. 100% coverage means the device can fully display all colors within that standard. Lower coverage indicates that some colors within the standard (typically certain saturated colors) cannot be displayed by the device and will appear duller or distorted.

2.3 Key Conclusions:
Large Volume ≠ Accurate Coverage: A monitor can have a very large gamut volume (e.g., 150% sRGB), but its coverage of the sRGB standard might only be 90%. This means it can display many vibrant colors outside sRGB, but simultaneously cannot accurately reproduce some colors within the sRGB standard. This is disastrous for color-critical work like photo editing.
High Coverage ≠ Large Volume: A monitor can achieve 100% coverage of the sRGB standard, but its total gamut volume might be only 100% sRGB. This means it can perfectly reproduce all sRGB colors but cannot display the more vibrant colors of P3 or Adobe RGB. This might be insufficient for professional photography or video post-production.
The Ideal State: For professional use, we typically prioritize "High Coverage" over "Large Volume." The primary goal is to ensure accurate reproduction of all colors within the target color space first, before pursuing a wider color range. A professional wide-gamut monitor should have a Gamut Volume ≥ Target Standard, while its Gamut Coverage is as close to 100% as possible.
In summary:
Look at "Coverage" to judge color accuracy.
Look at "Volume" to judge color vibrancy.