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This paper follows on paper 1250-06 in SPIE Proceedings of the 1990 Conference: 'Perceiving, measuring, and using color', Michael H. Brill, Chair/Editor, February 15-16, 1990. Visual efficiency of display devices, as well as of all other applications of strong visible coloration, demands an understanding of true spectral response of normal human vision, and for a useful colorimetry of visual processing. True spectral response of vision is considered unknown, while visual processing, in the sense represented by colorimetry, is thought to be adequately understood. It is the intent of this paper and its antecedent to suggest that both are mistaken: first, that spectral response is now fairly dependably known, and second that colorimetry works too poorly to support the contention that visual processing is understood well enough for that purpose. Fortunately, it appears that much of this understanding can be gained through psychophysics, without a good knowledge of the inner working of the visual system. We repeat here some evidence of true spectral response, and introduce new evidence on some ways in which visual processing does not occur. Colorimetry (measurement of color and brightness) does not correlate well to what the normal human observer sees. In researching the reasons for the discrepancies, we use (1) accurate, absolute spectral power distributions to arrive at power-content of viewed lights, (2) in a visual colorimeter coupled by a quartz light-pipe to a precise spectroradiometer; (3) three disparate primary-sets of three spectral lights; (4) six normal acute observers. Last year, we demonstrated large errors in computed chromaticity; this year we show that the errors are not largely due to the Standard Observer, but to the 'color-matching function' (CMF), and to its uses. Last year we suggested trouble with transformation of primaries; this year we show graphic evidence that transformation of primaries fails. The repercussions of these facts--failure of CMFs as weighting functions, and of transformation of primaries-- are unpleasant to contemplate. Avenues of possible improvement of the colorimetry situation are mentioned.
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