The calculation of weight factors for tristimulus integration

This article defines the method of calculation of weight sets for tristimulus integration published by the ASTM in its Method E 308–85. The preparation of weight sets for any measurement interval or wavelength range by Lagrange cubic interpolation from standard tables of data at other intervals is described. In addition, methods of truncating weight sets to wavelength ranges of less than 360 nm to 830 nm are discussed. The importance of calculating and maintaining the chromaticity of the neutral point is noted. An example of calculation of a set of weights is given in an Appendix, along with an example computer program that will calculate a set of weights at 20 nm intervals from standard illuminant‐observer data given at 1 nm intervals.