Thumbnail Sources

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.

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

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

If no cached thumbnail is found, and an image file contains an embedded thumbnail (jpeg files generated by digital cameras normally do), gThumb will attempt to use that. gThumb 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.

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

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

gThumb 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 dconf-editor. See the org.gnome.desktop.thumbnail_cache.maximum_age and org.gnome.desktop.thumbnail_cache.maximum_size keys in particular. Certain applications (like F-Spot) may automatically increase these settings greatly.