Is it ever possible for the output of a filter to be of a different size than the input?

If so, can you give me an example of how it's done. If not, at what point is the image forced back to the original size? Is it right at the end or some other point? Is this a limitation of GIMP's plugin interface?

Souphead.

Are you talking about the actual gimp plugin interface?

It's certainly possible with G'MIC, just by using any resize type command.
The gimp plugin interface is "deprecated" and will be moving to gegl (i.e. gegl buffers).
I suppose some example of use can be seen in gmic_gimp.cpp but there are docs about it elsewhere.

Edit: since you posted in G'MIC discussions, I'll assume you mean G'MIC

A basic resize example: -r 200%,200%

It just occurred to me you might be fighting with the "custom code" filter - it limits the size!

eg.
- Arrays & tiles > Array [regular] ...with Size = "Repeat [Memory consuming!]"
..resizes the input layer or creates a new layer/image which is NxM the size of the input layer
- Arrays & tiles > Montage

Yeah, the custom code filter got me. Just make it bigger, and there you go. Thanks garagecoder and jontait2.

Souphead.