Based on this code, it looks like we're doing ALL the scaling in imagemagick. Is that correct?

I don't think that's the long-term intended behavior. I think the long-term goal is to request different scalings from photoshop, getting a different pixmap for each scale factor. We want to do this specifically for cases where the image being generated is coming from vector layer(s). (But doing this all the time should be fine too).

This doesn't need to change for this code review. But, we should file a bug about it if my hunch is correct.