CHAPTER 4
258
Graphics
When a device color space is selected, the
ColorSpace
subdictionary of the cur-
rent resource dictionary (see Section 3.7.2, “Resource Dictionaries”) is checked
for the presence of an entry designating a corresponding default color space
(
DefaultGray
,
DefaultRGB
, or
DefaultCMYK
, corresponding to
DeviceGray
,
DeviceRGB
, or
DeviceCMYK
, respectively). If such an entry is present, its value is
used as the color space for the operation currently being performed. (If the appli-
cation does not recognize this color space, no remapping occurs; the original de-
vice color space is used.)
Color values in the original device color space are passed unchanged to the
default color space, which must have the same number of components as the
original space. The default color space should be chosen to be compatible with
the original, taking into account the components’ ranges and whether the compo-
nents are additive or subtractive. If a color value lies outside the range of the de-
fault color space, it is adjusted to the nearest valid value.
Note:
Any color space other than a
Lab
,
Indexed
, or
Pattern
color space may be used
as a default color space provided that it is compatible with the original device color
space as described above.
If the selected space is a special color space based on an underlying device color
space, the default color space is used in place of the underlying space. This applies
to the following color spaces:
•
The underlying color space of a
Pattern
color space
•
The base color space of an
Indexed
color space
•
The alternate color space of a
Separation
or
DeviceN
color space (but only if the
alternate color space is actually selected)
See Section 4.5.5, “Special Color Spaces,” for details on these color spaces.
Note:
There is no conversion of color values, such as a tint transformation, when us-
ing the default color space. Color values that are within the range of the device color
space might not be within the range of the default color space (particularly if the de-
fault is an
ICCBased
color space). In this case, the nearest values within the range of
the default space are used. For this reason, a
Lab
color space is not permitted as the
DefaultRGB
color space.