SECTION 4.5
255
Color Spaces
The terminology used in PDF color spaces and ICC color profiles is similar, but
sometimes the same terms are used with different meanings. For example, the
default value for each component in an
ICCBased
color space is 0. The range of
each color component is a function of the color space specified by the profile and
is indicated in the ICC specification. The ranges for several ICC color spaces are
shown in Table 4.19.
TABLE 4.19 Ranges for typical ICC color spaces
ICC COLOR SPACE
COMPONENT RANGES
Gray
RGB
CMYK
L*a*b*
[ 0.0 1.0 ]
[ 0.0 1.0 ]
[ 0.0 1.0 ]
L*:
[ 0 100 ];
a*
and
b*:
[
−128
127 ]
Since the
ICCBased
color space is being used as a source color space, only the “to
CIE” profile information (AToB in ICC terminology) is used; the “from CIE”
(BToA) information is ignored when present. An ICC profile may also specify a
rendering intent,
but PDF consumer applications ignore this information; the ren-
dering intent is specified in PDF by a separate parameter (see “Rendering Intents”
Note:
The requirements stated above apply to an
ICCBased
color space that is used
to specify the source colors of graphics objects. When such a space is used as the
blending color space for a transparency group in the transparent imaging model
(see Sections 7.2.3, “Blending Color Space”; 7.3, “Transparency Groups”; and 7.5.5,
(AToB)
and “from
CIE”
(BToA)
information. This is because the group color space is used as both the
destination for objects being painted within the group and the source for the
group’s results. ICC profiles are also used in specifying
output intents
for matching
the color characteristics of a PDF document with those of a target output device or
production environment. When used in this context, they are subject to still other
constraints on the “to CIE” and “from CIE” information; see Section 10.10.4,
The representations of
ICCBased
color spaces are less compact than
CalGray
,
CalRGB
, and
Lab
, but can represent a wider range of color spaces. In those cases
where a given color space can be expressed by more than one of the CIE-based