don't upscale images during thumbnail creation

There should be an option to not create new images when the thumbnail would generate an upscaled version, but return the original image instance instead.

I propose an upscale=False kwarg to image.thumbnail(), and plan to default it to True at some point in the future.

[xlotlu]

Oops, brain fart. I meant default True initially to preserve backwards-compatibility, and change it to False in the future. Sorry for the confusion.

Ideally there would be a nice deprecation warning for at least one version before that, django-style.

[nixjdm]

😕 I think we agree, actually. Let me double check / try to clarify.

so returning the original should be expected behaviour.

I think that is what I’m trying to say. It should be expected behavior, but currently isn’t. So short term we pave the way to fix it, and long term we actually fix it (and break backwards compatibility). Short term, keep default upscale=True to keep backwards compatibility (which currently is implicit), but add the feature upscale=False. Long term, break backwards compatibility by making upscale=False the default.

Perhaps we disagree about what to do for upscale=False? I’m not sure. I was saying that should return the original image, which I think you’re saying you want as well. The alternative is throwing an error.

Thanks for your patience hashing this out. It is a confusing topic.