SMPTE 2019: Metamerism, Color Ellipses, and Color Errors

This paper is about calculation of index of metamerism for the change of observer and comparisons with various color errors and tolerances.
There are two major aspects for color measure in visual reproduction. One goal is to measure the performance of reproduction equipment. The other aspect is related to the audience visual perception. On the one hand human perception is characterized by its variability and, on the other hand, technological trends in reproduction are adding new color source characteristics.
Metamerism is ensuring the viability of trichromatic reproduction. In fact, any reproduced color is rendered with a mix of three primaries. It is giving a perception similar to that of surfaces in front of the camera which have various complex spectra.
Various metamerism indexes have been defined to give a measure of the differences in color perception. The metameric index for change of observer is the most straightforward one; the CIE recommended method for it may be used to directly evaluate human perception variability found in any audience for a given reproduction system. At least this can be computed for a set of representative colors.
But new reproduction systems are based on primaries spectra differing sensibly from the ones previously used with Xenon light source. The method for calculation of the index of metamerism for change of observer is using the Standard Deviate Observer data in addition to the Standard Observer data.
The magnitude of color errors induced by this phenomenon is compared with JND found in MacAdam study. It is also compared with existing tolerances in color accuracy.
In fact, the tolerance expressed in current standards are much larger than the variations caused by the observer variability.
1 - In short, this paper will show how to calculate the index of metamerism for the change of observer; calculations are ending in magnitude of color errors.
2- The magnitudes of color error corresponding to MacAdam ellipses are calculated and compared to magnitude of indexes of metamerism.
3- Current color tolerances are also evaluated in terms of color errors.

Speaker:
Francois Helt-Toutous