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                                            252
CHAPTER 4                                                                Graphics



where the function g (x) is defined as
                                                6
g ( x ) = x3                                      -
                                        if x ≥ ----
                                               29

g ( x ) = ------- × ⎛ x – ---- ⎞
          108              4
                -            -           otherwise
          841 ⎝           29 ⎠

Example 4.8 defines the CIE 1976 L*a*b* space with the CCIR XA/11–
recommended D65 white point. The a* and b* components, although theoretical-
ly unbounded, are defined to lie in the useful range −128 to +127.

Example 4.8

   [ /Lab
            << /WhitePoint [ 0.9505 1.0000 1.0890 ]
               /Range [ −128 127 −128 127 ]
            >>
   ]


ICCBased Color Spaces

ICCBased color spaces (PDF 1.3) are based on a cross-platform color profile as
defined by the International Color Consortium (ICC). Unlike the CalGray,
CalRGB, and Lab color spaces, which are characterized by entries in the color
space dictionary, an ICCBased color space is characterized by a sequence of bytes
in a standard format. Details of the profile format can be found in the ICC speci-
fication (see the Bibliography).

An ICCBased color space is specified as an array:

   [ /ICCBased stream ]

The stream contains the ICC profile. Besides the usual entries common to all
streams (see Table 3.4 on page 62), the profile stream has the additional entries
listed in Table 4.16.

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