Step, the relationship between the step, gloss and measurement error
If the color measurement error is not caused by the measured sample. Then the accuracy of the instrument has little effect on the color difference data.
Sttocka has already pointed out in 1973 that for samples with high saturation, chromatic aberration can also be correctly calculated with 20nm step measurements. For example, the color difference of a pair of metameric samples is measured in steps of 10 nm and 20 nm, respectively. From the values ​​arranged in Table 2-3, the difference is very small.
It must be realized that for a sample with a significant difference between the two pairs of reflection curves, the color difference has only a slight change as a function of the step size. This change is far less important than changing the light source and changing the observer's influence. Not only are the chromatic aberrations still the same when calculating, but the tristimulus values ​​are still the same. In most cases, only the second decimal place is different. Therefore, it has been repeatedly stated that the requirement to manufacture a simplified spectrophotometer with a step size of 10 nm conforming to the technical level is certainly not an urgent matter.
Table 2-3 Effect of Step Size on Measurement
Metameric sample pairs ΔE(10nm) ΔE(20nm)
1 0.04 0.03
2 0.11 0.23
3 0.33 0.16
4 0.05 0.17
5 0.04 0.02
Table 2-4 Comparison with or without gloss correction D65/10°
The color difference of the sample under test Rmin a* b* The color difference between the sample and the reference sample ΔE*CIELAB
With or without belt Without belt Without belt
Red 23.8 38.6 40.9 14.0 15.2 0.73 0.81
Yellow 1 8.3 -14.7 -15.2 70.4 75.4 1.59 1.71
Yellow 2 7.8 0.3 0.3 76.6 84.5 0.33 0.34
Blue 16.8 -5.3 -5.8 -36.3 -38.7 0.46 0.50
Glossy samples are often observed with gloss excluded. The gloss is often measured together and then subtracted by a calculation method. The tristimulus value is reduced according to the gloss of the surface, and the reduced value is not more than 4 to increase the saturation. If trichromatic stimuli are directly calculated without considering the gloss correction problem when calculating the color difference, the tristimulus value is too large (approximately 4). Although the conversion of the tristimulus value color space is non-linear in the same color space, this error has no great influence on the color difference. If the color difference is calculated without performing the gloss correction, the color difference value is reduced by at most 0.1. Table 2-4 shows that the chromatic aberration obtained by considering the gloss correction and irrespective of the gloss correction is not significantly different; the values ​​of a* and b* are also given in the table, and the changes are obvious; the calculated values ​​of chromaticity are almost no different (samples) The difference in chroma from the reference sample is always insignificant). Nevertheless, it is not recommended to use a integrating sphere colorimeter with a gloss absorbing trap to measure samples with moderate gloss, because in this case the sample being compared may have different amounts of gloss eliminated.
Source: Shandong Printing Network