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SECTION 4.5                                                                 Color Spaces




              Decode ABC                        Decode LMN


          A                                L                                  X

          B                Matrix ABC      M                 Matrix LMN       Y

          C                                N                                  Z




        FIGURE 4.14 Component transformations in a CIE-based ABC color space


Color spaces in the CIE-based families are defined by an array

   [ name dictionary ]

where name is the name of the family and dictionary is a dictionary containing
parameters that further characterize the space. The entries in this dictionary have
specific interpretations that depend on the color space; some entries are required
and some are optional. See the sections on specific color space families, below, for
details.

Setting the current stroking or nonstroking color space to any CIE-based color
space initializes all components of the corresponding current color to 0.0 (unless
the range of valid values for a given component does not include 0.0, in which
case the nearest valid value is substituted.)

Note: The model and terminology used here—CIE-based ABC (above) and CIE-
based A (below)—are derived from the PostScript language, which supports these
color space families in their full generality. PDF supports specific useful cases of CIE-
based ABC and CIE-based A spaces; most others can be represented as ICCBased
spaces.

CalGray Color Spaces

A CalGray color space (PDF 1.1) is a special case of a single-component CIE-
based color space, known as a CIE-based A color space. This type of space is the
one-dimensional (and usually achromatic) analog of CIE-based ABC spaces.
Color values in a CIE-based A space have a single component, arbitrarily named
A. Figure 4.15 illustrates the transformations of the A component to X, Y, and Z
components of the CIE 1931 XYZ space.

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