That is when things always go wrong: when you try to ‘enlarge’ the image. The process seems to run out of video memory somewhere.
N.B. This ‘enlargement’ is an issue by itself, btw. And Topaz is doing it wrong. No offense. Seriously. What Topaz appears to be doing (which you can deduct from the time needed to create the Preview), is that they upscale the image first, and only then ‘crop to fill.’ This is bad (regardless of blotches), as it means the resultant image, pre-crop, is way larger than 3840 x 2160 (both in height and width), and only thereafter is cropped to fit the 4k constraints. And processing that surplus area takes a lot of extra time. Best is just to pre-crop first. On a 1080p source file, with say typical 140px black bars, you’d start by cropping 248px (140x1.77) from both sides, plus 140px from top and bottom, and only then do you upscale to 3840x2160. By pre-cropping, you avoid wasting time (and memory!) processing a much larger image first. This is a bit beyond the scope of this post, though, but I thought it was interesting to already mention.
I’m enhancing some old DVDs and I noticed occasional large, black splotchy artifacts generated by the Proteus model at settings of 300% scaling or above. (I couldn’t reproduce it in Artemis or Gaia, or Proteus at 200% or 100% scaling settings. But 300%+ shows the artifacts.)
If you’d like to try it for yourself, here’s the input file. It’s a lossless AVI in the YUV420 colorspace using the free “Lagarith” codec.
Thanks for looking into this. Proteus is the model I use 9 out of 10 times. I’ve seen other instances of these black splotches too, so this isn’t a one-in-a-million case.