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                                            478
    CHAPTER 6                                                                 Rendering



    5. Finally, scan conversion is performed to mark the appropriate pixels of the ras-
       ter output device with the requested colors.

    Once these operations have been performed for all graphics objects on the page,
    the resulting raster data is used to mark the physical output medium, such as
    pixels on a display or ink on a printed page. A PDF document specifies very little
    about the properties of the physical medium on which the output will be pro-
    duced; that information is obtained from the following sources:

    • The media box and a few other entries in the page dictionary (see Section
      10.10.1, “Page Boundaries”).
    • An interactive dialog conducted when the user requests viewing or printing.
    • A job ticket, either embedded in the PDF file or provided separately, specifying
      detailed instructions for imposing PDF pages onto media and for controlling
      special features of the output device. Various standards exist for the format of
      job tickets. Two of them, JDF (Job Definition Format) and PJTF (Portable Job
      Ticket Format), are described in the CIP4 document JDF Specification and in
      Adobe Technical Note #5620, Portable Job Ticket Format (see the Bibliography).

    Some of the rendering facilities described in this chapter are controlled by device-
    dependent graphics state parameters, listed in Table 4.3 on page 212. These pa-
    rameters can be changed by invoking the gs operator with a parameter dictionary
    containing entries shown in Table 4.8 on page 220.


6.1 CIE-Based Color to Device Color

    To render CIE-based colors on an output device, the consumer application must
    convert from the specified CIE-based color space to the device’s native color
    space (typically DeviceGray, DeviceRGB, or DeviceCMYK), taking into account the
    known properties of the device. As discussed in Section 4.5.4, “CIE-Based Color
    Spaces,” CIE-based color is based on a model of human color perception. The
    goal of CIE-based color rendering is to produce output in the device’s native color
    space that accurately reproduces the requested CIE-based color values as per-
    ceived by a human observer. CIE-based color specification and rendering are a
    feature of PDF 1.1 (CalGray, CalRGB, and Lab) and PDF 1.3 (ICCBased).

    The conversion from CIE-based color to device color is complex, and the theory
    on which it is based is beyond the scope of this book; see the Bibliography for
    sources of further information. The algorithm has many parameters, including an

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