According to the different structure, the color measurement
can be divided into two categories: one is the chroma meter, the other is the spectrophotometer.
1. Color meter
Color meter is a color measuring instrument which uses red, green and blue filters to decompose the reflected light of color samples, and then receives and converts it into color chroma value by sensors. In order to imitate the visual perception of human eyes and provide standard measurement values, standard light source must be used to illuminate the measured samples. The spectral sensitivity of the sensor needs to be converted through a filter to match the visual sensitivity of the standard observer. When the instrument is calibrated correctly, the measured values read by the color meter can be easily converted into three stimulus values of color.
The disadvantage of color meter is that the matching degree of spectrum between filter and sensor is impossible to achieve a true linear relationship in the strict sense with the sensitivity of human eyes to color vision. From this we can see that there is a theoretical error in the measurement of color by color meter, and the absolute accuracy of the measurement of color is not high.
Spectrophotometer is a color measuring instrument that uses grating to decompose the reflected light of color sample, and then receives the reflected spectrum through sensor and converts it into color chroma value. It measures all the visible reflectance spectra of a color sample, usually measuring a point every certain distance in the reflectance spectra, and some spectrophotometers can continuously measure the spectra.
Its working principle is that the color is measured as a physical phenomenon which is not controlled by the observer in order to obtain the stimulus value of the color. It integrates the reflection spectrum and interprets the color as a visual response. It is the most flexible color measurement instrument. At the same time, because the spectrophotometer is used to measure the total reflection spectrum of the color sample, the measurement results have higher absolute accuracy.