SECTION 7.6
563
Color Space and Rendering Issues
If a group’s color space—whether specified explicitly or inherited from the parent
group—is CIE-based, any use of device color spaces for painting objects is subject
to special treatment. Device colors cannot be painted directly into such a group,
since there is no generally defined method for converting them to the CIE-based
color space. This problem arises in the following cases:
•
DeviceGray
,
DeviceRGB
, and
DeviceCMYK
color spaces, unless remapped to de-
fault CIE-based color spaces (see “Default Color Spaces” on page 257)
•
Operators (such as
rg
) that specify a device color space implicitly, unless that
space is remapped
•
Special color spaces whose base or underlying space is a device color space, un-
less that space is remapped
It is recommended that the default color space remapping mechanism always be
employed when defining a transparency group whose color space is CIE-based. If a
device color is specified and is not remapped, it is converted to the CIE-based color
space in an implementation-dependent fashion, producing unpredictable results.
Note:
The foregoing restrictions do not apply if the group’s color space is implicitly
converted to
DeviceCMYK
, as discussed in “Implicit Conversion of CIE-Based Color
7.6.2 Spot Colors and Transparency
The foregoing discussion of color spaces has been concerned with
process colors—
those produced by combinations of an output device’s process colorants. Process
colors may be specified directly in the device’s native color space (such as
Device-
CMYK
), or they may be produced by conversion from some other color space,
such as a CIE-based (
CalRGB
or
ICCBased
) space. Whatever means is used to
specify them, process colors are subject to conversion to and from the group’s col-
or space.
A
spot color
is an additional color component, independent of those used to pro-
duce process colors. It may represent either an additional separation to be
produced or an additional colorant to be applied to the composite page (see “Sep-
The color component value, or
tint,
for a spot color specifies the concentration of
the corresponding spot colorant. Tints are conventionally represented as subtrac-
tive, rather than additive, values.