Chapter 4

Computing CIE Tristimulus Values

4.1 Introduction

In many manufacturing industries (such as plastics, textiles, and paints) trained experts known as colourists have traditionally been responsible for the assessment of the colour appearance of the colour match (Rich, 2002). Although this approach worked well for many years, in today's fast-moving global workplace more objective methods are required. Colorimetry attempts to capture the essence of colour perception and provides an objective procedure for accurate colour matching and reproduction. Tristimulus values are the basis of colorimetry and their accurate calculation is highly desired by industry for a wide range of applications. In order to compute the tristimulus values for a surface that is defined by a set of spectral reflectance factors it is necessary to specify an illuminant and a set of colour-matching functions. The spectral reflectance factors, the relative energy of the illuminant, and the colour-matching functions must be multiplied together at each wavelength and then summed. In some cases the reflectance factors are specified at a wavelength interval that is smaller or larger than the wavelength interval of the illuminant data or the colour-matching functions. This chapter reviews methods for computing tristimulus values from spectral reflectance data and considers the use of interpolation and extrapolation where appropriate.

4.2 Colour-Matching Functions

The CIE (see Section 1.3 for a brief review) ...

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