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SECTION 4.5                                                            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                                          % Color space
      [ /DeviceN
            [ /Cyan /Magenta /Black ]
            /DeviceCMYK
            15 0 R
      ]
   endobj

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