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                                        247
SECTION 4.5                                                           Color Spaces



The transformation defined by the Gamma and WhitePoint entries is
                   G
X = L = XW × A
               G
Y = M = YW × A
               G
Z = N = ZW × A

In other words, the A component is first decoded by the gamma function, and the
result is multiplied by the components of the white point to obtain the L, M, and
N components of the intermediate representation. Since there is no second stage,
the L, M, and N components are also the X, Y, and Z components of the final rep-
resentation.

The following examples illustrate interesting and useful special cases of CalGray
spaces. Example 4.5 establishes a space consisting of the Y dimension of the CIE
1931 XYZ space with the CCIR XA/11–recommended D65 white point.

Example 4.5

  [ /CalGray
        << /WhitePoint [ 0.9505 1.0000 1.0890 ] >>
  ]

Example 4.6 establishes a calibrated gray space with the CCIR XA/11–
recommended D65 white point and opto-electronic transfer function.

Example 4.6

  [ /CalGray
        << /WhitePoint [ 0.9505 1.0000 1.0890 ]
             /Gamma 2.222
        >>
  ]


CalRGB Color Spaces

A CalRGB color space is a CIE-based ABC color space with only one transforma-
tion stage instead of two. In this type of space, A, B, and C represent calibrated
red, green, and blue color values. These three color components must be in the
range 0.0 to 1.0; component values falling outside that range are adjusted to the
nearest valid value without error indication. The decoding functions (denoted by
“Decode ABC” in Figure 4.14 on page 245) are gamma functions whose coeffi-

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