Color rendering: Asking the question

Abstract

Two white lights may have the same chromaticity, and yet when used to light an array of objects may differ in their ability to reveal colors. For example, any white light can be matched by a mixture of two narrow-band lights, a yellow plus a blue. In this extreme case, reds and greens become black or brown and the red-green dimension is lost. At the other extreme, a light with three narrow bands, at the proper wavelengths, can brighten reds and greens and increase redgreen contrast, relative to a broad-band light such as daylight. Many commercial lights tend to dull reds and greens, relative to broad-band sources, a central reason that color rendering is a practical concern. A telling example is neodymium glass, a yellow-absorbing filter that is sometimes used to improve color rendering. This article seeks to bring these ideas to life through detailed graphical examples.

Applications of vectorial color

“…Emphasizing intuition and graphs rather than algebra, I reviewed the ideas of prime colors, color rendering, and projection matrix R, suggesting that they all relate to the overlap of receptor spectral sensitivities. 20 Then I made a discovery that ties R to the orthonormal basis, namely that the R equals the unity operator. 31 But that is almost the same as saying R = SS T .…”

“…A figure showed a view of a 3-dimensional graph. Problems that occur are mainly a matter of reds and greens 1,19,20 , making the v 1 -v 2 plane appropriate for a flat projection. Fig.…”

Color rendering: A calculation that estimates colorimetric shifts

“…Lights vary in their ability to render object properties into black-white and color contrasts 1 . A previous article 1 showed the systematic nature of color rendering effects that are likely to arise.…”

“…A previous article 1 showed the systematic nature of color rendering effects that are likely to arise. Owing to the spectral overlap of red and green cone sensitivities, a light can be achromatic-stimulating all three cone systems-if it has power in only two narrow bands, one in the blue and one in the yellow.…”

“…Jozef Cohen found that the smoothness of object reflectance spectra could be expressed by writing them as linear combinations of a few basis functions 3 . Extending that idea, he found that color matching functions themselves could be considered basis functions for any colored light, 4 combining to give the "fundamental metamer," and leading on to Matrix R 1,4 . Sherman Lee Guth and others have created simple quantitative opponent colors models 5 .…”