I wonder what @garagecoder is up to. Maybe he is a Nintendo dev. 
I still have a backlog of loose ends to look into in this thread, but I already have two questions that I have been waiting a very long time to ask.
1. In the paper, from what I could gather, the guided filter (which I love to use) could be used to transfer structures from image a to image b. My issue with the current implementation is that it is a blurring filter first. Any structure transferred is lost to the blur even when I use 1,1e-10. (As an aside, I see that apps like RawTherapee use radii that are less than one. Is it enlarging, filtering, then shrinking the image?) Another application is to refine masks. Again, I don’t know how to do what the paper shows.
2. Another question surfaced from my involvement with the PlayRaws. Take the recent one e.g., [PlayRaw] View from Fort Carré in France. There is text on the crane. When I down sample the image, it turns into an indiscernible blob. It looks like there are two groups that are equivalent: 1,4 and 2,3,5,6.
1=nearest | 2=average | 3=linear | 4=grid | 5=bicubic | 6=lanczos
Looks like IM has more possibilities but my head hurts from the reading.
– Resizing or Scaling -- IM v6 Examples
– Resampling Filters -- IM v6 Examples
– Nicolas Robidoux Resampling -- IM v6 Examples
I also found this paper that uses what is called detail-preserving image downscaling (DPID) from another paper. Their implementation doesn’t look complicated but I don’t have the math or dev chops to figure it out. 