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                                              343
      SECTION 4.8                                                                      Images



KEY             TYPE          VALUE

OC              dictionary    (Optional; PDF 1.5) An optional content group or optional content mem-
                              bership dictionary (see Section 4.10, “Optional Content”), specifying the
                              optional content properties for this image XObject. Before the image is
                              processed, its visibility is determined based on this entry. If it is deter-
                              mined to be invisible, the entire image is skipped, as if there were no Do
                              operator to invoke it.

      Example 4.28 defines an image 256 samples wide by 256 high, with 8 bits per
      sample in the DeviceGray color space. It paints the image on a page with its lower-
      left corner positioned at coordinates (45, 140) in current user space and scaled to
      a width and height of 132 user space units.

      Example 4.28

        20 0 obj                                      % Page object
           << /Type /Page
               /Parent 1 0 R
               /Resources 21 0 R
               /MediaBox [ 0 0 612 792 ]
               /Contents 23 0 R
           >>
        endobj

        21 0 obj                                      % Resource dictionary for page
           << /ProcSet [ /PDF /ImageB ]
               /XObject << /Im1 22 0 R >>
           >>
        endobj

        22 0 obj                                      % Image XObject
           << /Type /XObject
              /Subtype /Image
              /Width 256
              /Height 256
              /ColorSpace /DeviceGray
              /BitsPerComponent 8
              /Length 83183
              /Filter /ASCII85Decode
           >>

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