The Application of Projective Geometry to the Theory of Color Mixture

Consideration is first accorded to the basic problem of the mixture of two colors of given luminosities. It is shown that a simple geometric construction will enable determination of the point on the chromaticity diagram corresponding to the mixture for any values of relative luminosities of the two component colors forming the ingredients of the mixture. The method is next expanded to consider the case of color reproduction by the three-color process using three primaries. Laws governing the amount of luminosity contributed to a color mixture by each of the three primary components are deduced and shown to be of simple type. Comparison of the results of choice of different sets of primaries are discussed and illustrated. The performance of equiluminous primary systems, such as have been proposed for sequential color television, is examined critically. The color-fidelity limitations inherent in such a system are demonstrated and discussed. The luminosity demands of each primary in a three-color television system are next examined, using the geometric method of analysis. For two given primary systems (those known as primaries A and primaries C, respectively), curves are shown indicating the contours of maximum luminosity demand of each primary when functioning in the reproduction of the full gamut of reproducible colors on the chromaticity diagram. It is shown that the maximum luminosity demand of any primary does not necessarily occur during the reproduction of white.