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                                        260
CHAPTER 4                                                                   Graphics



  or space used within the group (see “Separation Color Spaces” on page 264 and
  “DeviceN Color Spaces” on page 268).
• Likewise, any uses of device color spaces for objects within such a transparency
  group have well-defined conversions to the group color space.

Note: A source color space can be specified directly (for example, with an ICCBased
color space) or indirectly using the default color space mechanism (for example,
DefaultCMYK; see “Default Color Spaces” on page 257). The implicit conversion of a
CIE-based color space to a device space should not depend on whether the CIE-
based space is specified directly or indirectly.


Rendering Intents

Although CIE-based color specifications are theoretically device-independent,
they are subject to practical limitations in the color reproduction capabilities of
the output device. Such limitations may sometimes require compromises to be
made among various properties of a color specification when rendering colors for
a given device. Specifying a rendering intent (PDF 1.1) allows a PDF file to set pri-
orities regarding which of these properties to preserve and which to sacrifice. For
example, the PDF file might request that colors falling within the output device’s
gamut (the range of colors it can reproduce) be rendered exactly while sacrificing
the accuracy of out-of-gamut colors, or that a scanned image such as a photo-
graph be rendered in a perceptually pleasing manner at the cost of strict colori-
metric accuracy.

Rendering intents are specified with the ri operator (see Section 4.3.3, “Graphics
State Operators”), the RI entry in a graphics state parameter dictionary (see Sec-
tion 4.3.4), and with the Intent entry in image dictionaries (Section 4.8.4, “Image
Dictionaries”). The value is a name identifying the rendering intent. Table 4.20
lists the standard rendering intents recognized in the initial release of PDF viewer
applications from Adobe Systems; Plate 5 illustrates their effects. These intents
have been deliberately chosen to correspond closely to those defined by the Inter-
national Color Consortium (ICC), an industry organization that has developed
standards for device-independent color. Note, however, that the exact set of ren-
dering intents supported may vary from one output device to another; a particu-
lar device may not support all possible intents or may support additional ones
beyond those listed in the table. If the application does not recognize the speci-
fied name, it uses the RelativeColorimetric intent by default.

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