SECTION 4.5
245
Color Spaces
Decode
ABC
Decode
LMN
A
B
C
Matrix
ABC
L
M
N
Matrix
LMN
X
Y
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.
A
component to
X, Y,
and
Z
components of the CIE 1931
XYZ
space.