The Measurement of Subjective Colour

Abstract

The measurement of subjective colour or colour appearance using the binocular matching technique is discussed. The colour appearance of objects which are an instrinsic part of a multi-element coloured scene have been measured using this technique and data are given showing quantitatively the effect of changes in illuminant colour, observer adaptation and scene environment on the subjective colour of the elements in the scene. Proposals are made for the development of a standard system for the measurement of subjective colour. IntroductionIt has been widely recognized [1-4] that such problems as the evaluation of the colour rendering properties of illuminants, the design of decorative lighting schemes, the determination of the optimum colour quality of colour reproduction systems, the effect of successive and simultaneous contrast on colour designs and the investigation of adaptation and after-images in visual research, require a method whereby the subjective colour or colour appearance of visual stimuli can be quantitatively described.The subjective colour of a visual stimulus is determined by the interaction of a number of physical, physiological and psychological factors. For isolated stimuli in the aperture mode, for example, the determining factors are the character of the light from the stimulus, the area of the stimulus and the adaptation state of the observer. When two or more stimuli are in the field of view, successive and simultaneous contrast effects can influence the colour appearance of the stimuli. For colours in the object mode, the colour is often considered to be the property of the object and as such is only one characteristic of appearance. Not only may the phenomenon of colour constancy begin to operate but appearance characteristics such as shape, size, surface structure may also influence the colour appearance of the object.A system of colour appearance specification must not only provide a quantitative measure of the major attributes of colour appearance, i.e., hue, saturation and luminosity, as they appear in a particular situation under the influence of the other attributes of appearance, but must also be capable of expressing the effect on colour appearance of changes in such factors as the characteristics and environment of the stimulus, colour constancy and contrast effects and the adaptation of the observer.