Color quality scale
The color quality scale ( English color quality scale , CQS) refers to a quantitative method for determining the color rendering of a light source . With the method, a spectrally measured light source receives a numerical value between 0 and 100. The index of a light source describes the rendering properties for color to a comparable reference light source . CQS was developed by NIST to replace the color rendering index R a , which has some deficiencies and is widely used . Similar to many other colorimetric evaluation criteria, the color quality scale evaluates the reproduction of individual standardized color samples.
history
The standardized color rendering index R a contains a very simple metric; it compares test and reference light sources using eight unsaturated color cards. The aim of its introduction was to evaluate the color fidelity of fluorescent lamps. This goal has been well met with this standard. However, he showed weaknesses when evaluating other light sources.
Various proposals were made to replace the color rendering index, but these could not replace the standard that had already been established. None of the proposals themselves have been standardized. Suggested replacement scales were:
- "8-band Spectral Band Method" derived from Full Radiator
- Flattery Index for Artificial Illumination (Deane Judd, 1967)
- Color Discrimination Index (Thornton, 1972)
- Color Preference Index (Thornton, 1974)
- Cone Surface Area (Fotios, 1997)
- Color rendering capacity (Xu, 1993)
- Feeling of Contrast Index (Hashimoto, Yano, Nayatani, 2000)
With the increasing proportion of LED light sources, changes in colorimetry became necessary, as the color rendering index puts certain LED light sources at a disadvantage compared to other light sources. Investigations on the subjective color impression showed the poor correlation between the perceived color quality and the color rendering index.
Differences to the color rendering index
In contrast to R a, the test colors of the color quality scale are all saturated. Only then is it possible to make a sound statement about the reproduction of saturated colors. The color quality scale is based on the assumption that the unsaturated colors are reproduced just as well by the light source due to scale effects. The newer approach succeeds by comparing it with a reference light source, but this is not regarded as the measure of all things , however, overemphasis on a color is not assessed negatively, i.e. not punished in the CQS. With the color quality scale, the numerical value is determined as the square mean - not as the arithmetic mean, as with the color rendering index. This leads to a greater devaluation of individual particularly poorly reproduced colors.
Individual evidence
- ↑ Yoshi Ohno, Wendy Davis (NIST): Rationale of Color Quality Scale (PDF; 854 kB)
- ^ Yoshi Ohno, Wendy Davis: Color Quality Scale . In: Optical Engineering 49 (3), 033602 (March 30, 2010). doi : 10.1117 / 1.3360335 .