Transactions of the Optical Society

The new international standards, which define a standard observer, three standard illuminants, standard conditions of illuminating and viewing opaque specimens, a standard for evaluating the brightness factor of opaque specimens, and a standard trichromatic system for the expression of colour measurements, are stated and their origin explained. In addition to the numerical tables which are appended to the resolutions setting up these standards, there are given a table specifying the trichromatic coordinates for the standard observer of all spectral colours at wave-length intervals of 1 mμ, tables to facilitate the calculation of the standard coordinates and the brightness factor of a material illuminated by any one of the three standard illuminants from spectrophotometric measurements on the material, and a table giving the coordinates of some stimuli of special importance on the N.P.L. system, the standard system, and another system which occurs in the resolutions. Some new colorimetric terms are proposed, partly to avoid misinterpretation and partly to meet new needs. The theory of colour transformations, and points which arise in the application of the system and in the calibration of instruments, are discussed.