A Standard for Thumbnailers

[Stanislav Brabec]

Sven Neumann wrote:
> Is the thumbnailer supposed to create PNG files that adhere to the
> thumbnailing standard? In other words, do the created thumbnail files
> have to include the comments that are required by the standard or does
> Nautilus add them later?

In practice, thumbnailer for Nautilus (and partially standard itself)
works but does not perform well in practice. I guess the standard should
avoid problems of Nautilus:

- Image files with several hardlinks are thumbnailed many times: once
  for each link
- Image files in symlinked directories are thumbnailed many times:
  once for each access path.
- Image files in public directories are thumbnailed many times:
  once for each accessing user.
- Thumbnails on removable media are thumbnailed many times: once for
  each machine, where medium is accessed
- Thumbnail files are often larger than images itself, especially for
  jpeg images below 20kB in size.
- Nautilus has no thumbnail management - several years used desktops
  often have ~/.thumbnails several gigabytes in size, often larger than
  the rest of the home directory.
- There is a very small chance to detect deleted images and delete
  corresponding thumbnail.
- Nautilus ignores embedded thumbnails and creates its own thumbnail.
  Embedded thumbnails are parts of many current image standards (EXIF,
  partial decoding of progressive jpeg, jpeg inlined mid-size preview
  from some digital cameras, tiff thumbnail, Kodak Photo CD files,...)


Few ideas:

Any application managing thumbnails must be able to create thumbnails
stored in the image directory.

Use unique inode_number/volume_id instead of file_path.

Haw widely used desktop-neutral thumbnailing library understanding many
embedded thumbnails and providing thumbnailing for images without
embedded thumbnail.

Allow jpeg thumbnails.

Thumbnails can use file system extended attributes.

-- 
Best Regards / S pozdravem,

Stanislav Brabec
software developer
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