People have been studying the characteristics of human eyes for a long time, measuring the spectral tristimulus value, putting forward the CIE standard observer and chromaticity system, and establishing the CIE1931 standard chromaticity system and CIE1964 supplementary standard chromaticity system. The design is based on the CIE1964 supplemental standard colorimetric system, which uses diffuse/vertical lighting/observation conditions, using halogen tungsten lamp + filter glass + photocell to simulate the D65+ standard observer to enable the fitting of spectral curves through the device.
Definition of chroma
In the color matching experiment, the color light to be measured can be a monochromatic light of a certain wavelength, also known as spectral color. A group of three stimulus values R, G and B can be obtained for monochromatic light of a corresponding wavelength. A series of similar matching experiments were carried out on the monochromatic light of different wavelengths to obtain the tristimulus values corresponding to the monochromatic light of different wavelengths. If the radiation energy of each monochromatic light is maintained to be the same (such spectral distribution is called isoenergetic spectrum), the tri-stimulus value obtained is called spectral tri-stimulus value.
Experiments have shown that almost any color can be mixed with certain primary colors of red, green and blue and that different people perceive the colors of light differently. To measure color more comparable, the international commission on illumination (ice) in 1964 proposed the XR 10(lambda), yr 10(lambda), or 10(lambda) standard chronometric observer spectral tri-stimulus curve, also called color matching function.
The reflected light depends on the reflection characteristics of the object surface, the geometric conditions of measurement, and the illumination source. The spectrum composition varies with these conditions. To calculate the reflected color of an object, the spectral composition of the light radiation entering the human eye must also be determined. Assume the relative spectral density of the light source with the sign s(lambda), the surface reflectance of the object with the sign t (lambda), or 10(lambda), yr 10(lambda), or 10(lambda) for the standard color 1964 standard observer's spectral tri-stimulus value. The tristimulus value can be expressed by the following formula:
K10 is the adjustment factor. Y10 not only represents the relative number of green primary colors but also represents the brightness factor of the object color. The color of an object's X10, Y10, or Z10 changes when the source of light, or the lambda, changes.
Spectral curves of tristimulus of standard observer spectrum of the colorimetric system, the higher the fitting degree, the more standard the measurement.
This is the principle of the precision color meter