Digital Color Management: Encoding Solutions, 2nd Edition

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Colorimetry

References made throughout this book to standard colorimetry, or to standard colorimetric values, refer to colorimetric values determined according to CIE (Commission Internationale de l'Éclairage) recommended practices. All standard colorimetric values shown have been determined using the color-matching functions for the CIE 1931 Standard Colorimetric Observer (Figure A.1), whose color-matching characteristics are representative of those of the human population having normal color vision. The CIE 1931 Standard Colorimetric Observer is often referred to as the 2° Observer, because test fields subtending a viewing angle of 2° were used in the judging experiments from which the color-matching functions were derived.

The CIE also has defined the 1964 Supplementary Standard Colorimetric Observer (Figure A.2), often referred to as the 10° Observer. The color-matching functions of the 10° Observer are used for colorimetric measurements and calculations related to relatively large areas of color. The color-matching functions of the 2° Observer are used for most colorimetric measurements and calculations related to pictorial and graphics imaging, where individual areas of color generally subtend relatively small viewing angles.

The 2° Observer color-matching functions are used in the calculation of CIE tristimulus values X, Y, and Z, which quantify the trichromatic characteristics of color stimuli. The X, Y, and Z tristimulus values for a given object (characterized by ...