Makes the dispatch to the chosen backend simpler in the thumbnails
plugin. Given that ArtResizer is not only about resizing art anymore,
these methods fit there quite nicely.
This didn't cause any issues since we only use the shared instance
anyway, but logically it doesn't make a lot of sense for the backends
always using ArtResizer.shared (which they should be oblivious of).
remove interlacing by default when resizing/down-scaling, the
`deinterlace` option is to remove interlace when otherwise no processing
would have happened.
Squashed from the PR, relevant commit messages follow below:
Added file size option to artresizer
- In line with comments on PR, adjusted the ArtResizer API to add
functionality to "resize to X bytes" through `max_filesize` arg
- Adjustment to changelog.rst to include max_filesize change to ArtResizer
and addition of new plugin.
Added explicit tests for PIL & Imagemagick Methods
- Checks new resizing functions do reduce the filesize of images
Expose max_filesize logic to fetchart plugin
- Add syspath escaping for OS cross compatibility
- Return smaller PIL image even if max filesize not reached.
- Test resize logic against known smaller filesize (//2)
- Pass integer (not float) quality argument to PIL
- Remove Pillow from dependencies
- Implement "max_filesize" fetchart option, including
logic to resize and rescale if maxwidth is also set.
Added tests & documentation for fetchart additions.
Tests now check that a target filesize is reached with a
higher initial quality (a difficult check to pass).
With a starting quality of 95% PIL takes 4 iterations to succeed
in lowering the example cover image to 90% its original size.
To cover all bases, the PIL loop has been changed to 5 iterations
in the worst case, and the documentation altered to reflect the
50% loss in quality this implies. This seems reasonable as users
concerned about performance would most likely be persuaded to
install ImageMagick, or remove the maximum filesize constraint.
The previous 30% figure was arbitrary.
