VIII. The colour sensations in terms of luminosity

Abstract

My attention has been directed recently to the theoretical considerations involved in the production of photographs in approximately the colours of Nature, by combining together the images from three positives backed by appropriate colour screens, the colours chosen being those which should best represent the three Colour Sensations of the Young Theory. During my investigations into the matter I found it necessary to ascertain what these colours were, for although serious objections may be raised to the Young Theory when considering it in detail, yet when expressed in a general form it adequately explains the phenomena which arise when colours fall upon the centre of the retina. The sensation curves have been given by Kœnig, but it appeared that a redetermination by a luminosity method might well be undertaken, for they did not altogether agree with the results of some preliminary measures that I had made in order to trace them. In my work on ‘Colour Vision’ I have given a rough diagram as to what the sensation curves might be when they are shown as luminosities which together make up the total luminosity of the spectrum of the crater of the arc light, but it was only intended to be an approximation to the correct diagram. The method, however, by which the problem could be attacked and by which a rigid determination could be made was indicated. It is by this method that the results given in the following pages have been obtained.