SECTION 4.5
285
Color Spaces
Note:
Not all devices support overprinting. Furthermore, many PostScript printers
support it only when separations are being produced, and not for composite output.
If overprinting is not supported, the value of the overprint parameter is ignored.
An additional graphics state parameter, the
overprint mode (PDF 1.3),
affects the
interpretation of a tint value of 0.0 for a color component in a
DeviceCMYK
color
space when overprinting is enabled. This parameter is controlled by the
OPM
entry in a graphics state parameter dictionary; it has an effect only when the over-
print parameter is
true
, as described above.
When colors are specified in a
DeviceCMYK
color space and the native color space
of the output device is also
DeviceCMYK
, each of the source color components
controls the corresponding device colorant directly. Ordinarily, each source color
component value replaces the value previously painted for the corresponding de-
vice colorant, no matter what the new value is; this is the default behavior, speci-
fied by overprint mode 0.
When the overprint mode is 1 (also called
nonzero overprint mode),
a tint value of
0.0 for a source color component leaves the corresponding component of the
previously painted color unchanged. The effect is equivalent to painting in a
DeviceN
color space that includes only those components whose values are non-
zero. For example, if the overprint parameter is
true
and the overprint mode is 1,
the operation
0. 2 0. 3 0.0 1.0 k
is equivalent to
0. 2 0. 3 1.0 scn
in the color space shown in Example 4.22.
Example 4.22
10 0 obj
[ /DeviceN
[ /Cyan /Magenta /Black ]
/DeviceCMYK
15 0 R
]
endobj
% Color space