@afre to help a little with those questions:
- The “structure transfer” does seem to work as described in the paper, certainly if you test with a binary filter used on a guide image. For example try this:
gmic sp teddy n 0,1 +norm otsu. 256 median. 5 +guided. ..,5,0.01
- From memory G’MIC uses a box average when downscaling, depending on the interpolation chosen. Perhaps for linear, bicubic and lanczos. DPID apparently uses an inverse bilateral filter, maybe not so easy. Perhaps it could be approximated by a “bilateral sharpen” (see the many tone/detail filters) before downscale. I’ve read downscaling frequently has greater debate than upscale…