Colour displays in image processing admit grey scales as well as colour scales for the visual representation of image information. Pseudocolours can be used to enhance the discriminability of different parts of the image. Luminance scales, on the other hand, are preferred for representing fine detail as human colour vision is limited to relatively low spatial frequencies. In the present paper, the generation of quantitative luminance and colour scales with CRT displays is discussed. This includes the colour characteristics of CRTs as well as a recapitulation of the CIE 1931 (X, Y, Z) tristimulus colorimetry system. The CIE 1976 UCS diagram (u', v') is used as an approximation to a perceptually uniform representation of chromaticity. On this basis, it is shown how, for each pixel, luminance and colour (hue) can be chosen independently. In order to add colour as a further visual dimension to greyscale images, a set of equiluminant hues is proposed for each luminance level. The hues are chosen from equidistant steps around a circle in the (u', v') chromaticity diagram. This choice of colours is particularly suitable for the visual representation of a cyclic quantity like phase angle.