I have been travelling and thus missed the opportunity to make a timely contribution. As you know, I am absolutely delighted with this new addition of dual-demosaic to RT.
I’m not entirely certain what you meant regarding how to manually choose the ideal threshold amount for demosaicing. I am wondering if the selection mask preview could be solely activated for demosaic, and not require jumping to Detail>Sharpening etc. and going back. My preference is not to use RT to perform any sharpening, so I have to make the additional step to go and turn it off again.
I seem to get the impression that the sharpening contrast threshold should be set to 7 or 8, and then one should zoom in a lot to say 300% or more, look hard and increase the demosaic threshold settings in increments of 1, and observe for when no more subtle changes are visible. It is not easily noticeable at first, until one knows what to look out for. I see tiny changes happening along edges of the contrast mask. Is that how one should judge the threshold amount in your opinion?
I made a big layered TIFF in Photoshop so I could compare the results with DCB+VNG4 with threshold settings in increments of 1 through to 10, and 12, 15, 20 etc. It’s difficult to say which is indeed the most optimal result. My own old and rather unrefined technique to manually blend DCB with VNG4 in Photoshop was to use the “Find Edges” filter to make a mask, and using curves to increase the contrast so there is maximum rejection or reveal of said demosaic layer. This method gives approximately the same result as a threshold of 20. While my own eyes picked 8 as the optimal result before I did this comparison. I can see that in some regions the threshold 8 retains a touch more detail, although there were also subtly more artifacts. None of which should be visible in a print.
The image I was testing on is attached as a raw file in this message. It does not contain clear and smooth regions, rather it has out-of-focus parts. It was shot with a macro lens at f/8, a7R II at ISO 100. It is one of several frames in a focus-stacked sequence, in a panoramic stitched sequence. When I use the ‘Automatic’ checkbox, the algorithm returned a threshold recommendation of “0”, which clearly isn’t what I needed. Strange that the algorithm is not able to pick up the out-of-focus regions as flat regions which require blending with VNG4.
I have also been thinking that even in an image which has no or hardly any smooth regions and is in focus everywhere, a threshold of zero is unlikely to give an optimal result. This can be seen in the underexposed shadows of this autumn leaves raw file, which on the right edge, while sharp, still benefits from the less artifacty VNG4, albeit only slightly. I find it interesting that my preference for a threshold value of 8 in this file is right in the middle of the range you mentioned of 7-10 for D700 ISO 100 files. Perhaps the automatic function should default to a 7 or so if it returns a 0 result.
I see on Github that you considered removing manual override totally. I would not vote for that for the excellent reasons you provided there youself, all three apply in my case.
_DSC1267.ARW (82.3 MB)