Color inconstancy index (CON), well stablished and recommended by the ISO 105-J05 normative, is usually applied on textile solid colors, and not on gonio-apparent ones. In this work we propose a fast and easy implementation and virtual color assessment of this colorimetric index for these innovative colors, often used in many industries as automotive, cosmetics, computer graphics, plastics for electronic consumers, printing inks, etc. Instead using the ΔE CMC(1:1) color difference formula, the ΔE AUDI2000 formula for the six measurement geometries recommended by the ASTM E2194 normative was used simulating the theoretical visual assessment in a directional lighting booth, and applied on some different panel sets, as the official AUDI palette composed by 117 colors, both solid, metallic and pearlescent. The theoretical directional lighting booth can select different standard illuminants (A, D65 as reference, and F11), daylight fluorescent simulators (D50, etc.) and light sources (as wLED, etc.). The results showed that spectral reflectances with low chroma and lightness lead to minimum CON index. But, spectral reflectances with high chroma and middle lightness lead to maximum CON index. Additional interesting conclusions were also derived. For instance, for near-specular geometries the CON index is maximum due the high variability or contrast in the photometric scale of the spectral reflectance (higher to the conventional 100 %). Although the spectral content of the light source clearly influences on the CON index of a color panel, different relative spectra can provide different color travels in the same panel, and then high CON index, as for instance A vs. D65, or F11 and D65, or wLED vs. D65. Consequently, depending on the industrial application and the end use (light & color interaction), the CON index for each color recipe (even design) can be analyzed in advance as a new colorimetric feature of any colored material.
Francisco M. Martínez-Verdú, Esther Perales, Elisabet Chorro, Valentín Viqueira, Bárbara Micó-Vicent, Omar Gómez;, "Theoretical Implementation of the Color Inconstancy Index for Gonio-Apparent Automotive Coatings" in Proc. IS&T 23rd Color and Imaging Conf., 2015, pp 255 - 261, https://doi.org/10.2352/CIC.2015.23.1.art00046