SECTION 7.6
575
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.