Color Rendering Index (CRI)
Color viewing, even near the D50 standard color temperature, is only as accurate as the quality of the light source. The CRI, or color rendering index, is a quantitative scale which measures the quality of color shown by a light source. This is based on how colors appear to the human eye and how clearly visible variations in color are. The CRI scale ranges from 0 to 100, with higher CRI values being equivalent to better quality color representation under a light source when compared to a reference. A light source with a CRI of 100 is used as a reference for comparison to measure CRI in another light source with the same color temperature. Color shifts are observed for eight specified colors in a sample image. A colored image or object will exhibit color shifts under light sources with varying color rendering indices, even though their color temperatures are the same. For the purposes of color viewing, a high CRI alone may be misleading, as the relative CRI of two light sources is only valid if they have the same color temperature. Some light source manufacturers may promote their products as having a high CRI value, but CRI is irrelevant for graphic arts and photography industry color viewing if the light source is not at the accepted D50 standard. Because of this, the International Commission on Illumination (CIE) has created a standard of tolerance known as the CIE chromaticity diagram. Chromaticity is an aspect of color defined by its dominant wavelength and purity. These properties are used to create coordinates, as compared to a reference, on a chromaticity diagram.
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