The experimental results were combined into the specification of the CIE RGB color space, from which the CIE XYZ color space was derived. Thus, three parameters corresponding to levels of stimulus of the three kinds of cone cells, in principle describe any human colour out of space pdf sensation.
In some color spaces, including the LMS and XYZ spaces, the primary colors used are not real colors in the sense that they cannot be generated in any light spectrum. The CIE XYZ color space encompasses all color sensations that are visible to a person with average eyesight. It serves as a standard reference against which many other color spaces are defined. Consider two light sources composed of different mixtures of various wavelengths. Certain tristimulus values are thus physically impossible, for example LMS tristimulus values that are non-zero for the M component and zero for both the L and S components. Furthermore, LMS tristimulus values for pure spectral colors would, in any normal trichromatic additive color space, e.
The CIE 1931 color space defines the resulting tristimulus values, in which they are denoted by “X”, “Y”, and “Z”. The XYZ tristimulus values are thus analogous to, but different from, the LMS cone responses of the human eye. The reflective and transmissive cases are very similar to the emissive case, with a few differences. The CIE 1931 color space chromaticity diagram. RGB colors may not be displayed properly either. For example, the color white is a bright color, while the color grey is considered to be a less bright version of that same white.
In other words, the chromaticity of white and grey are the same while their brightness differs. CIE xyY color space and is widely used to specify colors in practice. The figure on the right shows the related chromaticity diagram. Note that the chromaticity diagram is a tool to specify how the human eye will experience light with a given spectrum. The diagram represents all of the chromaticities visible to the average person. The gamut of all visible chromaticities on the CIE plot is the tongue-shaped or horseshoe-shaped figure shown in color. These colors, although they are on the border of the gamut, have no counterpart in monochromatic light.
Less saturated colors appear in the interior of the figure with white at the center. If one chooses any two points of color on the chromaticity diagram, then all the colors that lie in a straight line between the two points can be formed by mixing these two colors. In more general terms, a distance on the CIE xy chromaticity diagram does not correspond to the degree of difference between two colors. Although they were a distinct improvement over the CIE 1931 system, they were not completely free of distortion. It can be seen that, given three real sources, these sources cannot cover the gamut of human vision. These formulas can be derived from the previously presented definitions of x and y chromaticity coordinates by taking advantage of the fact that the tristimulus values X, Y, and Z of the individual mixture components are directly additive.
Not all test colors could be matched using this technique. When this was the case, a variable amount of one of the primaries could be added to the test color, and a match with the remaining two primaries was carried out with the variable color spot. For these cases, the amount of the primary added to the test color was considered to be a negative value. In this way, the entire range of human color perception could be covered. When the test colors were monochromatic, a plot could be made of the amount of each primary used as a function of the wavelength of the test color. The CIE 1931 RGB color matching functions.
The color matching functions are the amounts of primaries needed to match the monochromatic test color at the wavelength shown on the horizontal scale. The color matching functions are the amounts of primaries needed to match the monochromatic test primary. 1931 was difficult to reproduce as a monochromatic beam, was chosen because the eye’s perception of color is rather unchanging at this wavelength, and therefore small errors in wavelength of this primary would have little effect on the results. The color matching functions and primaries were settled upon by a CIE special commission after considerable deliberation. Note that rather than specify the brightness of each primary, the curves are normalized to have constant area beneath them. The resulting normalized color matching functions are then scaled in the r:g:b ratio of 1:4. By proposing that the primaries be standardized, the CIE established an international system of objective color notation.