Abstract
The color difference meter has three photodetectors, each with a separate tristimulus filter, and each receiving some of the light reflected from the specimen. Signals from the photodetectors are measured by analog circuits that give rectangular coordinates for surface colors in close correspondence to their positions in uniform color space. The first model described in 1948 uses barrier-layer photocells and three tristimulus filters. Recently, a model employing vacuum phototubes and four filters has been built. Use of vacuum phototubes makes it possible to substitute a dc amplifier and pivot meter for the suspension galvanometer necessary with barrier-layer photocells. By thermostatting the phototube chamber, excellent stability is obtained. A light pipe in the viewing beam provides a more stable and efficient mixer of light to the different photodetectors than the white-lined sphere used previously.
© 1958 Optical Society of America
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Richard S. Hunter
J. Opt. Soc. Am. 48(9) 597-605 (1958)
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