Determination of colorimetric uncertainties in the spectrophotometric measurement of colour

A method for the determination of colorimetric uncertainties has been developed in order to meet the requirements for accreditation by the UK accreditation service (UKAS), which include a statement of uncertainty for all certified quantities. The values of the principal sources of spectrophotometric uncertainty are first determined and are used to calculate corresponding components of colorimetric uncertainty using a simple model. The components of uncertainty analysed are 100% level (diffuse reflectance), photometric non-linearity, dark level and wavelength error. Bandwidth error is not significant for NPL surface colour standards because a small bandwidth is always used.

The gloss trap error and specular beam error are determined and corrected so that only the uncertainties after correction need be considered. These can be treated as components of dark level uncertainty. The uncertainties are determined for the following colour data: x, y, Y, u′, v′, L^*, a^* and b^* for the CIE 10° Standard Observer and the CIE Standard Illuminant D₆₅ for three geometries: specular included, specular excluded and 0°/45°. These are now quoted routinely on NPL certificates for ceramic colour standards, white and black ceramic tile standards and Russian opal standards.