Chromaticity Points of Real Spectra Outside the CIE Chromaticity Diagram

When an expert in colorimetry is asked whether the chromaticity point of a real spectrum can fall outside the CIE xy chromaticity diagram, the immediate answer will probably be something like “No! That is not possible!” Comprehensive investigations revealed that the concept of convexity is violated in several specific regions of the chromaticity diagram. Given that the deviations are only visible at the 5th decimal place, the results do not influence most calculations or practical measurements. However, since a fundamental property—convexity—of the chromaticity diagram relevant to the theory of colorimetry has been disproved, the color matching functions must be revised to maintain theoretical integrity.