Take advantage of Pillow's "reducing_gap" argument

[johanneskoch]

Hiya! Thanks for providing django-imagekit and pilkit. We've noticed that thumbnailing huge images (~320 megapixels) is extremely heavy and we've experienced timeouts due to this.

Pillow 7.0.0 introduced a new "reducing_gap" argument that makes resizing these large images a lot more efficient: https://pillow.readthedocs.io/en/stable/releasenotes/7.0.0.html#new-argument-reducing-gap-for-image-resize-and-image-thumbnail-methods

I'll probably be forking and applying this change myself, so I can make a pull-request at that point. What's this project's philosophy on supporting older Pillow/PIL versions? I obviously have no need of backwards-compatibility for my own purposes.

[vstoykov]

Hi! Thank you for your interest in django-imagekit and pilkit. Normally we are kind of conservative about backward compatibility. Probably I need to see what it the version bundled in the major distributions which are still supported and aim for that. I suppose that Pillow there will be lower than 7.

If the usage of reducing_gap can be made optional (use it if available) then this will be perfect.