Comparison of Color Measurement

1. Color measurement
When comparing the chromatic aberrations of two color samples, the influence of absolute accuracy error of the color measurement instrument on the chromatic aberration belongs to higher order error. Therefore, when comparing two color samples with the same color measurement instrument, the chromatic aberration caused by the error of absolute accuracy of the instrument itself is usually negligible. The reason is that the absolute accuracy error is included in the measurement value of two color samples when measuring two color samples. When calculating and comparing the color difference, the influence of the absolute accuracy error is reduced.

However, the absolute accuracy deviation of some middle and low-grade color measurement is so large that the color difference between two samples with large color difference can not be neglected. This kind of color measurement can only be used to compare two samples with very small difference, such as controlling the consistency of ink in a batch of printed matter.

Therefore, in printing, the color measurement used to control color consistency can achieve satisfactory results. There are other situations in actual production. If two color measurement with low absolute accuracy are used, even if the color difference of samples with small difference in Metamerism is not negligible.

2. The influence of measurement step on the measurement accuracy of spectrophotometer
Spectrophotometers measure the color of a sample by integrating its reflection spectrum. In fact, most spectrophotometers usually measure a point every 10 or 20 nm in the reflection spectrum. In theory, the smaller the separation step is, the more accurate the Chroma value is.

In fact, a pair of samples with distinct differences in spectral reflectance curves have only slight changes in chromatic aberration as a step function. The experimental results also show that the three stimulus values are the same as the color difference measured by spectrophotometers with measuring steps of 10 and 20 nm, respectively. In most cases, the difference in measurement results occurs only after the second decimal point.

People may observe color samples under different light sources, but spectrophotometers always use the same light source to measure color. Therefore, the influence of measuring step distance is less than that of changing light source or observer. Printing is to copy the color and tone of original manuscript with three primary color inks. Therefore, printing and original manuscript are the most common phenomena of Metamerism. From the above analysis, it can be seen that it is more important to determine which illumination source is used to compare the color difference between the original and the printed matter than to reduce the measurement step of the spectrophotometer.