(note) CIE chromaticity diagram

Chromaticity diagram (chromaticity diagram)： By the international lighting Commission in 1931 Made in .

Through chromaticity diagram , We can know the proportion of the three primary colors that make up a certain color , You can also see the complementary color of this color 、 Lightness and saturation .

CIE Chromaticity diagram （chromaticity diagram,CIE）：

CIE Chromaticity diagram is made of CIE Chromaticity coordinates x and y The two-dimensional graph drawn .x Is the horizontal axis ,y Is the vertical axis . The outer boundary of visible light is defined by the point where the spectrum is located , The arched curve consists of pure 380nm To 770nm The spectral color of . Chromaticity diagram defines the color gamut of color equipment by depicting and comparing the relationship between light source and white dot of display .

Chromaticity diagram is a functional expression of blackbody trajectory v=f（u） In colorimetry, a plan view expressed in chromaticity coordinates . The light color changes of different temperatures of blackbody form an arc track on the chromaticity diagram, which is called Planck track or blackbody track . The application of colorimetric system is communicating with people 、 transmission 、 To study the needs of color information, a variety of distinctive color systems have been established. This study adopts CIE1931 Standard colorimetric system and CIE1976 Uniform color space .

from 380nm To 780nm The spectral color of is CIE 1931 RGB The trace on the chromaticity diagram is shown in the following figure ：

And all the colors that human eyes can recognize , They are all composed of monochromatic light , Therefore, the range covered by the line drawn by any two points on the chromaticity curve , Namely “ All colors that the human eye can see ” Area size of . This is the limit of human eye resolution .

Fill this area with color , It's like this ：

Look for the , The line below , yes 380nm and 780nm Connection of . It forms another boundary of the color gamut .

however , The curve of the upper boundary is one-to-one corresponding to monochromatic light , However, the straight line of the lower boundary does not correspond to monochromatic light , It's a mixture of two spectral colors . Because it is a mixture of red and blue , So it's mainly purple . It means , There is no purple formed by monochromatic light . All purple colors , What purplish red , magenta , It's all about “ Out of spectrum color ”.（ Is this the reason why purple makes people feel mysterious ？）

Any new color mixed with two monochromatic lights , Or just step on the spectral track , Or it is within the area surrounded by the spectral trajectory , Never go outside .

after CIE Deliberate design , When XYZ When the tristimulus value reaches an equilibrium state , It will form white . be located （x=0.3333, y=0.3333） The point of location , It represents that the three primary colors occupy each other 1/3, Is an ideal isoenergetic white light E. This large area in the middle , They are all different white . That is, the saturation is 0 Fading of （ It may be black , It may also be white ）.

among , Except for those specially used for theoretical research 、 The imaginary waiting energy white light E Beyond the point , There is also a very important white point ：C spot . Its full name is CIE Standard light source C, Equivalent to the color of the sun at noon .（ Pay attention to the chromaticity diagram , The light source C and E Are not far apart ,C Slightly more E Higher color temperature .）

Reference：

Chromaticity diagram _ Comprehensive analysis of chromaticity diagram - Let you know about chromaticity diagram