The RGB values become unpleasant when the values of RGB representation are negative. It is defined in 1931 in base terms of virtual primary axes X, Y and Z. This axes are used to allow to match all visible colors as linear combination with positive coefficient only. Hence it is known as the chromaticity values X, Y, Z. The visible colors can be expressed as the C=XX+YY+ZZ. The normalization processed and it becomes X+Y+Z=1. This gives new coordinates as x, y and z =1-x-y which are independent on luminous energy X+Y+Z. The coordinates of visible chromatic value form a horseshoe shaped region with the spectrally pure colors on the curved boundary. Following figure 4.3 (a) shows the horseshoe shape of the visible region. Fig. no. 4.3 (a)
Following is the figure 4.3 (b) of CIE chromaticity. Fig. no. 4.3 (b) |
It is used in pipeline video, digital photography systems. It is also reffered as YPb/Cb Pr/Cr, Y’CbCr. Y’ is the luma component and Cb and Cr are the blue ab=nd red difference chroma components. Y’ is difeered by Y i. e. luminance (light intensity is nonlinear based on gamma corrected RGB primaries) This color space can defined by mathematical coordinate transformation from associated RGB colors. Following figure 4.3 (d) shows the representation of RGB to YCbCr transformation. Fig. no. 4.3 (d) |