The structure of the colorimeter is not the same. In order to reduce the blindness of the instruments purchased by the enterprise, this paper analyzes the characteristics of each instrument according to the measurement principle of different colorimeter, and based on the purpose of enterprise quality control. Some basis for purchasing a colorimeter is proposed, in order to provide some help to the company when it is introduced.
Principle of color measurement
Depending on the structure, the colorimeter can be divided into two categories: one is a colorimeter and the other is a spectrophotometer.
1. colorimeter
The colorimeter is a color measuring instrument that uses the red, green, and blue color filters to decompose the reflected light of the color sample, and then receives the converted color chromaticity value through the sensor. In order to mimic the visual perception of the human eye in order to provide a standard-compliant measurement, the sample to be measured must be illuminated with a standard light source. The spectral sensitivity of the sensor needs to be converted by the color filter to match the visual sensitivity of the standard observer. When the instrument is correctly calibrated, the measured value read by the colorimeter is easily converted into the tristimulus value of the color.
The disadvantage of the colorimeter is that it is impossible to achieve a true linear relationship in the strict sense of the degree of matching between the color filter and the sensor and the sensitivity of the human eye to the color visual perception. It can be seen that the colorimeter has a principle error in measuring the color, and the absolute accuracy of the measured color is not high.
2. Spectrophotometer
A spectrophotometer is a colorimetric instrument that uses a grating to decompose the reflected light of a color sample and then receives the reflected spectrum through a sensor and converts it into a color chromaticity value. It measures the total visible reflection spectrum of a color sample, usually measuring a point at a certain distance in the reflection spectrum, and some spectrophotometers can continuously measure the spectrum.
It works by measuring color as a physical phenomenon that is not dominated by the observer. In order to obtain the tristimulus value of the color, it can integrate the reflection spectrum and explain the color as a visual response. Flexible color measuring instruments. At the same time, since the spectrophotometer measures the entire reflection spectrum of the color sample, the measurement result has higher absolute precision.
Color measurement comparison
When comparing the color difference of two color samples, the absolute accuracy error of the colorimeter is a high-order deviation, so when comparing the two color samples with the same colorimeter, the absolute accuracy of the instrument itself is caused by the error. The color difference is usually negligible. The reason is that the colorimeter will contain the absolute accuracy error in the measurement of the two color samples when measuring two color samples. When calculating the color difference, the influence of the absolute precision error is reduced.
However, some medium and low-grade colorimeters have large absolute precision deviations, so that the color difference produced when comparing two color samples with large color difference can not be ignored. Such colorimeter can only be used to compare two different colors with different colors. different spectral sample, such as a number of printed products ink consistency control this is the case, so the printing, the colorimeter for controlling color consistent performance satisfactory results.
There are other situations in actual production. If two colorimeters with low absolute precision are used, even if the color difference of the color samples with different differences is different, the color difference can not be ignored.
2. Influence of measuring step size on measurement accuracy of spectrophotometer
The spectrophotometer measures the color by integrating the reflection spectrum of the sample. In fact, most spectrophotometers usually measure a point every 10 nm or 20 nm on the reflection spectrum, and then sum the tristimulus values ​​of the color. In theory, The smaller the separation step, the more accurate the measured chromaticity value.
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