The determination of uncertainty in spectrophoto metric surface colour measurement.

This paper reports on work undertaken by nine European laboratories as part of a European Commission funded research project. The project's goal was to improve harmonisation of international colorimetric scales. One objective of the exercise was to devise a means of expressing total uncertainty in colour measurement. When measuring colour (or indeed any physical quantity), an assessment of the uncertainty of the result is as important as the value itself. This fact, long recognised in physics, is increasingly important to any quality assured organisation that relies on measurements. The approach described first determines values of the sources of spectrophotometric uncertainty, and uses a simple model to combine these into total colorimetric uncertainties. The model has been used to determine uncertainties for the following colour data: x, y, Y, u', v', L*, a* and b* for the CIE 10degrees Standard Observer and the CIE Standard Illuminant D-65 for three geometries: specular included, specular excluded and 0degrees/45degrees. The method is used routinely at NPL in its UKAS accredited calibration services.