Principle of three primary colors of colorimeter

We know that the main purpose of the research and development of colorimeter is to detect the color of products and control the color quality of products. To better analyze and manage color information, it is necessary to understand the color. The change of color is closely related to color. To learn color, we should first know what the three primary colors are.

The colorimeter detects the product color according to its color light ternary principle and complementary color principle. The essence of the three primary colors is independent, and none of the three primary colors can be combined with the other two colors. In addition, as the basic color of color, the three primary colors can be mixed into various colors through the color gamut. During the formation of color perception, the color of light source is related to the three factors of light source, eyes and brain. Therefore, the selection of the three primary colors of color light involves such factors as the wavelength and energy of light source, and the spectral response range of human eyes. This is also a detail that must be paid attention to in the development process of the colorimeter.

However, from the energy point of view, the mixed brightness superposition of colored light means that the mixed colored light must be brighter than all the colored lights before mixing. Only the colored light with low brightness can be mixed into a large number of colors. Otherwise, the colored light with high brightness can be used as the primary color, and its addition will be brighter, so that the colored light with low brightness can never be mixed. In addition, we also know that the three primary colors are distributed in different areas of the visible spectrum. If they are concentrated in a certain area, they will not be able to mix more colored light.

In the white light dispersion experiment of the colorimeter, we can observe that the red, green and blue colors are more evenly distributed in the whole visible spectrum, and occupy a wide area. However, if we adjust the prism angle of the experiment to narrow the spectrum, we will find that the area occupied by the corresponding colored light will also change. In the color experiment of the colorimeter, on the narrowed spectrum, it will be found that the obvious red, green, and blue light changes most significantly, and the other light colors gradually fade, and some are about to disappear. The wavelength ranges of three kinds of colored light can be obtained through experiments: R (600~700nm), G (500~570nm), B (400~470nm).

In chromatics, the whole visible spectrum is generally divided into blue light area, green light area and red light area for research. When red light, green light and blue light are mixed, yellow light, cyan light and magenta light can be obtained respectively. Magenta light is not found in the spectrum, and we call it extraspectral color. If we mix the three colors equally, we can get white light; By mixing the three colored lights in different proportions, a variety of different colored lights can be obtained.

Because the colorimeter is an instrument developed to simulate the principle of human eyes to see color, the visual physiological characteristics must not be ignored when analyzing color light and three primary colors. When the human eye looks at an object, there are three kinds of color sensitive cells in the retina — red cells, green cells, and blue cells. These three cells are sensitive to red light, green light, and blue light, respectively. When one of the color sensitive cells is strongly stimulated, it will cause the excitement of the color sensitive cells, and then the color feeling will be generated. Similarly, in the color measurement process of the colorimeter, when the instrument receives a red light stimulus, it will send a red message to the instrument’s microprocessor. The three color sensing cells of the human eye have the ability to combine colors. When a polychromatic light stimulates the human eye, the color sensing cells of the human eye can decompose it into red, green and blue monochromatic light, and then mix them into a color. It is precisely because of this color combination ability that we can recognize a wider range of colors except red, green and blue.

To sum up, we can determine that there are three basic colored lights in the colored light, and their colors are red, green and blue. These three kinds of colored light are not only the main colored light obtained after white light decomposition, but also the main component of mixed colored light, and can match the spectral response range of human eye retinal cells, which is consistent with the visual physiological effect of the human eye. These three kinds of colored lights are mixed in different proportions, and almost all the colored lights in nature can be obtained, with the largest mixed color gamut; Moreover, these three colors are independent. One of the primary colors cannot be mixed with the other primary colors. Therefore, we call red, green and blue the three primary colors of color light. In order to unify the understanding, the International Commission on Illumination (CIE) stipulated the wavelength of three primary colors in 1931 λ R=700.0nm, λ G=546.1nm, λ B=435.8nm。 In the research of chromatics, in order to facilitate the qualitative analysis, white light is often regarded as a combination of red, green and blue primary colors.

There are many places involving chromatic light and three primary colors in the use of chromatic aberration meter, not only these simple conceptual problems. There are more complex analysis and comparison, but those are more professional knowledge. We are involved in different aspects in the process of using the colorimeter. Therefore, as long as we are familiar with these primary color concepts, we can better measure and understand the test results.

Color measurement system of colorimeter:
Color model is a set of rules and definitions that describe all colors in a simple way in the development and use of color difference instrument. Among them, color space is the most common example of color models. We often say that CIE LAB, CIE XYZ, RGB and CMYK are color models. The cataloging system assigns a unique name or number to each color. Such as Munsell color system, Pantone color card, etc.
However, in the color difference instrument industry, the use of Munsell color system is higher. The Munsell system divides the three-dimensional color space into three axes: hue, brightness and chroma. This system is very powerful in terms of order, but it does not provide the coordinate system needed for color space description of the colorimeter. Based on this disadvantage, the CIE color system developed by colorimeters converts any spectral curve into three letters, which become trichromatic values X, Y, Z. When Y is associated with light, X and Z are independent of hue and chromaticity.

Chromaticity diagram developed by CIE

Colorimeter CIE 1976 LAB chromaticity space:
CIE1976LAB color space is usually called CIE LAB in the color difference instrument industry. It is also called CIE L * a * b * in many colorimetric literatures. CIE LAB is currently the international color measurement standard and the most widely used chromaticity space in the color industry. This color space uses coordinates to mark chromaticity values, which is called chromaticity coordinates. The idea of using color coordinates comes from the fact that colors are not both red and green or both blue and yellow, but colors can be considered as combinations of red and yellow, red and blue, and green and blue.

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