Attentive friends may have discovered that among the many parameters of the colorimeter, there is a reflectance factor measurement range, which will have an impact on the color measurement results of the instrument. So, what is the reflectance measurement range of the colorimeter?What is the effect on color aberration?The following is an introduction for you, interested friends may wish to learn about it!
The essence of the colorimeter color measurement method is to measure the spectral reflectance factor of opaque objects by comparative method, and measure the spectral photometric characteristics of the sample by quantitatively comparing the spectral power of the complete diffuse reflector and the sample at the same wavelength, and the spectral reflectance factor of the complete diffuse reflector is 1 at each wavelength, that is, r( )=1 or r( )=100%. Usually the spectral reflectance factor of an object does not exceed 100%. However, for objects containing fluorescent substances, the spectral reflectance factor of fluorescent colors often exceeds 100% at certain wavelengths. Moreover, considering that the diffuse reflectance characteristics of the actual object are not Lambertian bodies, the effect of its gloss under certain measurement conditions will also make the measured spectral reflectance factor exceed 100%.
In the design of the instrument, the detector response at the measurement of spectral reflectance factor r( )=100% is usually not close to saturation, but there is often a margin to meet the needs of higher spectral reflectance factor measurement. As a result, most instruments currently set the reflectance factor measurement range to 0 200%. For example, the TS7036 has a reflectance factor measurement range of 0 200%.
In some cases, the measured spectral reflectance factor changes the same proportion of the photometry at each wavelength compared to the true value, i.e., the spectral reflectance factor shifts up (down) as a whole. This situation is mainly caused by changes in measurement conditions, such as changes in the actual measurement position of the analyte and the ideal measurement position (caused by jitter during the measurement), or changes in the output power of the light source, resulting in changes in the incident spectral flux and reflected spectral flux of the analyte, which is usually independent of wavelength. In addition, the radiometric calibration error leads to the measurement linearity error of the instrument, which will cause the measured value and the true value to produce the same proportion of error at each wavelength.
Taking the spectral reflectance factor r0( )=1 of a complete diffuse reflector as an example, a series of errors of the same proportion are introduced into the luminosity of each wavelength at the same time, and the resulting chromatic aberration e*ab in the CIELAB color space is calculated. When the relative error is 1%, the new spectral reflectance factor r1( )=101, its color difference e*ab will be different. It can be seen that the overall introduction of a 1% error in the spectral reflectance factor luminosity of a complete diffuse reflector can cause a chromatic aberration of about 04。
Due to the introduction of the same error in the spectral reflectance factor of each wavelength of the complete diffuse reflector, in the 1931 system or the 1964 system, the chromatic aberration is almost the same under the four conditions of standard illuminator A or D65, and after changing the test conditions, it can be found that the chromatic aberration is almost linear with the photometric error of the spectral reflectance factor.
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