Definition: Measure of colour quality of something seen: its hue and saturation. * Given by chromaticity coordinates of visual stimulus where value for e.g. red in coordinate is ratio between stimulus from red and sum of stimuli from red, green, blue. Colours with same hue and saturation have same chromaticity coordinates, but may vary in luminance (or brightness). * Chromaticity and luminance fully define colour of visual stimulus. * May also be defined in terms of dominant wavelength and purity of colour of visual stimulus.
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