Previous Next

                                                588
      CHAPTER 8                                                           Interactive Features



      The thumbnail image for a page is an image XObject specified by the Thumb
      entry in the page object (see “Page Objects” on page 144). It has the usual struc-
      ture for an image dictionary (Section 4.8.4, “Image Dictionaries”), but only the
      Width, Height, ColorSpace, BitsPerComponent, and Decode entries are signifi-
      cant; all of the other entries listed in Table 4.39 on page 340 are ignored if present.
      (If a Subtype entry is specified, its value must be Image.) The image’s color space
      must be either DeviceGray or DeviceRGB, or an Indexed space based on one of
      these. Example 8.2 shows a typical thumbnail image definition.

      Example 8.2

         12 0 obj
             << /Width 76
                /Height 99
                /ColorSpace /DeviceRGB
                /BitsPerComponent 8
                /Length 13 0 R
                /Filter [ /ASCII85Decode /DCTDecode ]
             >>
         stream
         s4IA>!"M;*Ddm8XA,lT0!!3,S!/(=R!<E3%!<N<(!WrK*!WrN,
         … Omitted data …
         endstream
         endobj

         13 0 obj                                      % Length of stream
            …
         endobj


8.2.4 Collections

      Beginning with PDF 1.7, PDF documents can specify how a viewer application’s
      user interface presents collections of file attachments, where the attachments are
      related in structure or content. Such a presentation is called a portable collection.
      The intent of portable collections is to present, sort, and search collections of relat-
      ed documents, such as email archives, photo collections, and engineering bid
      sets. There is no requirement that files in a collection have an implicit relation-
      ship or even a similarity; however, showing differentiating characteristics of relat-
      ed documents can be helpful for document navigation.

Previous Next