Color measures of chromaticity diagrams

Brightness, hue and saturation are called the three characteristics of color vision. Brightness is the degree of brightness; Hue is the color determined by the wavelength, for example, the hue of 700nm light is red, the hue of 579nm light is yellow, the hue of 510nm light is green, etc.; Saturation is purity, a narrow-band single-band signal that is not mixed with white. Color, visually speaking, is a color with high saturation. All light in the spectrum is the purest color light. The more white you add, the less pure the mixed color will be and the less saturated it will look. The International Commission on Illumination (CIE) formulated a chromaticity diagram in 1931, which uses the ratio of the three primary colors that make up a certain color to specify this color. That is, the ratio of the sum of the three primary colors is used to represent a certain color, and it can be written as an equation: (Color)=R(R)+G(G)+B(B) In the formula, (C) represents a certain color, (R), (G), and (B) are the three primary colors of red, green, and blue. R, G, and B are the proportion coefficients of each color. Their sum is equal to 1, that is, R+G+B=1. "C" means matching, that is, the color is visually the same. For example, a certain blue-green can be expressed as: (C)=0.06(R)+0.31(G)+0.63(B) If it is a mixture of two primary colors, one of the three coefficients is zero; if it matches white, R, G, and B should be equal. Any color is specified by the ratio of the three primary colors that match that color, so each color occupies a certain position in the chromaticity diagram. In the chromaticity diagram: the X-axis chromaticity coordinate is equivalent to the proportion of the red primary color; the Y-axis chromaticity coordinate is equivalent to the proportion of the green primary color. There is no Z-axis chromaticity coordinate (that is, the proportion of the blue primary color) in the figure. Because the proportion coefficient X+Y+Z=1, the Z coordinate value can be calculated, that is, 1-(X+Y)=Z. The CIE1931 chromaticity diagram developed by the International Commission on Light is shown in Figure 31. Each point on the arc curve in the chromaticity diagram is the various colors on the spectrum, that is, the spectral locus, and is the chromaticity coordinate of each color in the spectrum. The red band is in the lower right part of the figure, the green band is in the upper left corner, and the blue-violet band is in the lower left part of the figure. The straight line at the bottom of the figure, that is, the straight line connecting 400nm and 700nm, is a series from purple to red that is not found in the spectrum. C near the center of the picture is white, which is equivalent to the color of sunlight at noon. Its chromaticity coordinates are X=0.3101, Y=0.3162, and Z=0.3737. Suppose there is a color S on the chromaticity diagram. Draw a straight line from C through S to the spectral locus O point (590nm). The dominant wavelength of the S color is 590nm. The color of the spectrum here is the hue of S (orange). The distance from point C to the spectral trajectory of a certain color indicates its color purity, that is, saturation. The closer the color is to C, the less pure it is, and the closer it is to the spectral locus, the purer it is. Point S is located at 45% of the spectrum trajectory from C to 590nm, so its color purity is 45% (color purity % = (CS/CO) × 100. Draw a straight line from any point on the spectrum trajectory through C to reach the opposite spectrum At a point on the trajectory, the colors at both ends of this straight line are complementary colors (dashed line). Draw a straight line from any point in the purple-red segment through point C to a point on the opposite side of the spectral trajectory. This non-spectral color is represented by the complementary color of the spectral color. The representation method is to add a C after the wavelength of the complementary color of the non-spectral color, such as 536G. This purple-red color is the complementary color of 536nm green. The CIE1931 chromaticity diagram has great practical value, regardless of the light source color. Surface colors can be calibrated on this chromaticity diagram, which makes the description of color simple and accurate. For example, in order to ensure the correct identification of color marks and the control of traffic safety, a specific range is specified on the CIE1931 chromaticity diagram. , it is suitable for the encoding of various warning signals and color signs. For example, on the CIE1931 chromaticity diagram, various intermediate colors obtained by mixing two colors can be derived, such as the addition of Q and S, resulting in Q to. The various intermediate colors of the S line, such as point T, reach the spectral color of 552nm from C through T. The hue of T can be seen from the wavelength color of 552nm, and it can be seen from the position of T between C and the 552nm spectral color. In practical applications, such as color television, color photography (latex processing) or other color reproduction systems, it is necessary to select the appropriate three primary colors of red (R), green (G) and blue (B) for reproduction. For white and various colors, the positions of the selected (R), (G), and (B) on the chromaticity diagram should form a triangle so that the (R), (G), and (B) triangles should be as inclusive as possible. Large area, while (R), (G), (B) lines should be as close as possible to the spectral locus to reproduce more saturated red, green, blue and other colors.