How red is red? In many display applications, there are strict requirements on the accuracy and precision of color measurement. To accurately measure color, its degree of difficulty is indeed beyond people’s imagination. The medical and aerospace fields have extremely demanding display requirements. Not only does it need to display the color truly and reliably to transmit the most basic information about the color of the object, but also the color control system must have accurate color data so that the control can be effectively implemented. Currently, both display product manufacturers and consumers trust the measurements given by color measuring instruments, including colorimeters and spectroradiometers.
In many cases, people tend to accept or reject the results of the relevant display measured by the instrument without considering the accuracy of the measurement. If the monitor’s colorimetric measurements are inaccurate, it is likely that the user will adopt a product that is not of perfect quality, and that he will reject a product that is quite good.
In order to use an instrument more efficiently, one needs to know the accuracy of its measurements, and the same is true for a colorimeter. People need to know if the color measurement system is perfect and can do the inspections that people need it to do.
The product data includes conventional technical error values: the color coordinates x, y are 0.002; the lightness is 2%. It should be noted that these nominal values given may be misinterpreted, especially for display measurements. Because these nominal values are based on measurements made on an incandescent light source with a color temperature of approximately 2856K. The spectral power distribution of this light source approximates the distribution of the A standard light source specified by the International Commission on Illumination (CIE), which is a standard light source commonly used in photometry and colorimetry.
Calibrating with this type of light source currently has some problems. If this type of instrument is used to measure a light source with a spectral power distribution similar to that of a light source, accurate results can be expected. However, people often want to look at the spectral distribution of some displays whose chromaticity and luminance are quite different from A light source. The test results show that the accuracy of the color measuring instrument will change quite obviously, which has a great relationship with the spectral distribution of the measured color.

In the case of pocket colorimeters employing three-pass or four-pass band detectors (referred to as tristimulus colorimeters), the spectral response of each passband and the color matching function (x, y, z) specified by the International Commission on Illumination) are not very well matched. Therefore, measuring different spectral distributions with this instrument will generate errors.
When measuring with an array spectroradiometer, there are also a series of factors that affect the accuracy of color measurement, including stray light, wavelength calibration errors, and the linearity of the detector array.
Error analysis is complex no matter what type of device is used, and, for a variety of different displays and different colors, the errors of colorimetric instruments are often not known in advance. Although the instrument is accurately calibrated against an incandescent light source, it is not known how accurate it will be when it is used to measure the colorimetric and luminance of a display’s color.
Experience shows how serious this problem can be. If several colorimeters are used to measure the chromaticity of different colors of a display, people will find that the measurement results of each colorimeter are different. %, which is related to the color and type of monitor being tested. This difference is an order of magnitude greater than the calibration error stated by the instrument manufacturer, and indicates that some commercial instruments are at this level of error when measuring the color of a display. Color measurement errors are indeed too large for many common commercial, industrial, and military applications.
In many applications, the calibration method based solely on the incandescent light source cannot meet the actual requirements of the display. Therefore, a new calibration method is proposed for a special colorimeter for display measurement.
During the calibration process, the various colors of the actual display are measured with the caliber 4mm handheld color meter and spectroradiometer under test and a reference instrument for direct comparison to complete the calibration. According to the calibration results, any color of the display can be measured with a calibrated colorimeter under the condition of known chromaticity and luminance errors.
