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Webvision: Color Perception <br />500rim. (S)=G+B-R <br />Page 6 of 18 <br />Figaro S. The use of Nmlon's colour circle to illustrate rnatchin2 a spectral colour of 500 run usinu the three privnaric.. (9F�jpea imae�_ <br />In order to deal with the 'negative' colours, the CIE devised the XYZ system that uses unreal (imaginary) <br />primaries to describe colour space. The 1931 CIE chromaticity system chose three imaginary primaries <br />(reference stimuli) X, Y and Z, so that all spectral loci lying inside this triangle will be positive. The <br />alychne are locus of colours with no luminosity and this was chosen to lie along the X to Z on the XYZ <br />chromaticity system. All luminosity is expressed in Y. The reference loci of Y was chosen to just <br />enclose the domain of real colours. Equi -energy white was chosen to have equal chromaticity co- <br />ordinates, that is, 0.33, 0.33 (figure 9 and 10). Chromaticity co-ordinates represents the relative <br />contribution of the three primaries, the sum of the co-ordinates equals 1.0. Therefore, z can be <br />calculated, by knowing the co-ordinates x and y since x + y + z = 1. <br />P <br />Vision. 2"`le$. Landon: C3ianman tinct hall, 1.9GS. {qt Fi iP_ca.image.Phi]atiel i;__L%, Sar�nderc Com ,rani: 19jR, i�6ii jp imace� <br />Dominant wavelength, complementary wavelength and excitation purity can be easily located for a <br />sample. The dominant wavelength represents the principle wavelength of the colour. The <br />complementary wavelength is the wavelength that produces white when mixed in appropriate portions <br />with the dominant wavelength. Spectral complementaries can be found when a line joined by a lines <br />which passes through the achromatic point shown as C (figure 11). The dominant wavelength of A is <br />given by the spectral wavelength at DA and the complementary by the wavelength at CA (figure 11). <br />Point C identifies the location of the white point and B identifies another wavelength, that when mixed <br />at the appropriate proportions, will produce white. <br />http://www.webvision.med.utah.edu/KallColor.html <br />6/18/01 <br />