ISO 18314-3:2022

Overview

ISO 18314-3:2022 - Analytical colorimetry - Part 3: Special indices defines standardized methods to calculate one‑dimensional colour indices used to describe lightness/jetness and chromatic shifts (chroma/hue) within a single colour coordinate. It applies to tristimulus values and chromaticity coordinates derived from the standard CIE colorimetric systems (CIE 1931 2° and CIE 1964 10° observers) and is intended for specifying reflecting or transmitting colour stimuli where a single index is required.

Key topics and technical requirements

• Scope and input data
  • Indices are calculated from tristimulus values X, Y, Z or chromaticity x, y using CIE 1931 (2°) or CIE 1964 (10°) colour‑matching functions.
  • Standard illuminant D65 is used for parameters in several indices.
• Defined special indices
  • CIE whiteness index (W): formula uses chromaticity offsets with parameters x and y given for D65 (values provided for 2° and 10° observers).
  • Yellowness index (YI): linear combination of X and Z relative to Y with parameters a and b specified for 2° and 10° observers (follows ASTM E313 practice).
  • Blackness values (M, M_C): hue‑independent and hue‑dependent blackness expressed as logarithmic functions of Y or combinations of X, Z, Y (DIN 55979 references). Absolute hue contribution dM quantifies blue vs. brown bias.
  • Greyness values (G, G_C): analogous hue‑independent and hue‑dependent measures for grey admixture; absolute contribution dG describes hue bias.
  • Flop‑index (FI): characterizes angular variation of lightness for near‑neutral metallic shades using specified CIELAB L*(ε) at aspecular angles (ε = 15°, 45°, 110°).
• Measurement and metrology guidance
  • Recommendation for spectral photometer with 45°:0° (or 0°:45°) geometry; standard D65‑like artificial illumination for visual assessments.
  • Repeatability requirement example: variance of standard Y shall be