hi, if you want, absolutely do play around with K. in my tests it did not lead to any better denoising. to my surprise a larger K often led to worse results (for some reason often the relevance of discovered patches decreases with distance from the current point). that's why K is not exposed in the gui, no need for another irrelevant and cryptic parameter. if you find a compelling case where this indeed leads to better denoising we could rethink that.
in general NLM is a 0-th order denoising scheme, meaning the prior is piecewise constant (you claim the pixels you find are trying to express /the same/ mean, so you average them). if you let that algorithm do what it would really like to, it'll create unpleasant blotches of constant areas. so for best results we need to tone it down one way or another. cheers, jo On Fri, Jan 26, 2018 at 7:36 AM, rawfiner <rawfi...@gmail.com> wrote: > Hi > > I am surprised to see that we cannot control the neighborhood parameter for > the NLM algorithm (neither for the denoise non local mean, nor for the > denoise profiled) from the GUI. > I see in the code (denoiseprofile.c) this TODO that I don't understand: "// > TODO: fixed K to use adaptive size trading variance and bias!" > And just some lines after that: "// TODO: adaptive K tests here!" > (K is the neighborhood parameter of the NLM algorithm). > > In practice, I think that being able to change the neighborhood parameter > allows to have a better noise reduction for one image. > For example, choosing a bigger K allows to reduce the spotted aspect that > one can get on high ISO images. > > Of course, increasing K increase computational time, but I think we could > find an acceptable range that would still be useful. > > > Is there any reason for not letting the user control the neighborhood > parameter in the GUI ? > Also, do you understand the TODOs ? > I feel that we would probably get better denoising by fixing these, but I > don't understand them. > > I can spend some time on these TODOs, or to add the K parameter to the > interface if you think it is worth it (I think so but it is only my personal > opinion), but I have to understand what the TODOs mean before > > Thank you for your help > > rawfiner > > ___________________________________________________________________________ > darktable developer mailing list to unsubscribe send a mail to > darktable-dev+unsubscr...@lists.darktable.org ___________________________________________________________________________ darktable developer mailing list to unsubscribe send a mail to darktable-dev+unsubscr...@lists.darktable.org
