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<page xmlns="http://projectmallard.org/1.0/" type="topic" id="gthumb-thumbnails" lang="zh_CN">
  <info>
    <link type="guide" xref="index#reference"/>
  </info>
  <title>Thumbnail Sources</title>

  <p>The browser window normally shows the thumbnails of the images
  and movies in the selected folder. Generic icons for other files
  (audio files, for instance) may also be shown.</p>

  <p>You can select what types of files to show in the browser view
  using the <guiseq><gui>View</gui><gui>Filter</gui>
  </guiseq> dialog. The default is to show all media files (images,
  movies, audio), but this can be made more or less
  restrictive.</p>

  <p>The thumbnails may be generated by a number of different
  methods. <app>gThumb</app> will first check for existing thumbnails in the
  system cache.</p>

  <p>If no cached thumbnail is found, and an image file contains an
  embedded thumbnail (jpeg files generated by digital cameras
  normally do), <app>gThumb</app> will attempt to use that. <app>gThumb</app> will
  confirm that the aspect ratio of the thumbnail is similar to that
  of the main image, and ignore thumbnails that do not appear to
  match the main image.</p>

  <p>If that doesn't work, <app>gThumb</app> will attempt to load the entire
  file and generate a scaled-down thumbnail.</p>

  <p>Lastly, <app>gThumb</app> will use any system-defined scripts for
  thumbnailing particular media types. For example, some systems
  may use <app>mplayer</app> or <app>totem</app> or other movie viewers to generate movie
  thumbnails.</p>

  <p><app>gThumb</app> will save thumbnails to a system cache, to share them
  with other applications. By default, Gnome systems prune cached
  thumbnails when they are older than 180 days, or when the
  thumbnail cache exceeds 512 MB. Technically-inclined users can
  explore these settings with <app>dconf-editor</app>. See the
  org.gnome.desktop.thumbnail_cache.maximum_age and
  org.gnome.desktop.thumbnail_cache.maximum_size keys in particular.
  Certain applications (like <app>F-Spot</app>) may automatically increase
  these settings greatly.</p>
</page>
