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SECTION 7.6                                            Color Space and Rendering Issues



In all cases, the rendering intent to use for converting an object’s color (whether
that of an elementary object or of a transparency group) is determined by the ren-
dering intent parameter associated with the object. In particular:

• When painting an elementary object with a CIE-based color into a transpar-
  ency group having a different color space, the rendering intent used is the cur-
  rent rendering intent in effect in the graphics state at the time of the painting
  operation.
• When painting a transparency group whose color space is CIE-based into a
  parent group having a different color space, the rendering intent used is the
  current rendering intent in effect at the time the Do operator is applied to the
  group.
• When the color space of the page group is CIE-based, the rendering intent used
  to convert colors to the native color space of the output device is the default
  rendering intent for the page.

Note: Since there may be one or more nested transparency groups having different
CIE-based color spaces, the color of an elementary source object may be converted to
the device color space in multiple stages, controlled by the rendering intent in effect
at each stage. The proper choice of rendering intent at each stage depends on the rel-
ative gamuts of the source and target color spaces. It is specified explicitly by the doc-
ument producer, not prescribed by the PDF specification, since no single policy for
managing rendering intents is appropriate for all situations.

A similar approach works for the black-generation and undercolor-removal func-
tions, which are applied only during conversion from DeviceRGB to DeviceCMYK
color spaces:

• When painting an elementary object with a       DeviceRGB color directly into a
  transparency group whose color space is DeviceCMYK, the functions used are
  the current black-generation and undercolor-removal functions in effect in the
  graphics state at the time of the painting operation.
• When painting a transparency group whose color space is DeviceRGB into a
  parent group whose color space is DeviceCMYK, the functions used are the ones
  in effect at the time the Do operator is applied to the group.
• When the color space of the page group is        DeviceRGB and the native color
  space of the output device is DeviceCMYK, the functions used to convert colors
  to the device’s color space are the default functions for the page.

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