On Thu, Nov 3, 2016 at 6:59 PM, KOVÁCS István <k...@kovacs-telekes.org> wrote: > The HSV-based solutions look inferior to me. Last September, I started > a thread, but it did not get far. See the message quoted below - the > sample images are available at > http://tech.kovacs-telekes.org/files/dt_profiled_denoise_colour_vs_hsv_colour/ > > Thanks, > Kofa > > > > ---------- Forwarded message ---------- > From: Stéphane Gourichon <stephane_darkta...@gourichon.org> > Date: 12 September 2015 at 09:19 > Subject: Re: [Darktable-users] profiled denoise - colour vs HSV colour > To: darktable-us...@lists.sourceforge.net > > > Le 11/09/2015 22:44, KOVÁCS István a écrit : > > Even when fit to the screen (1920x1080), I find the plain > 'colour'-blended version (DSC_8834.jpg) less noisy *and* sharper than > the HSV-colour-blended one (DSC_8834_01.jpg). Zoomed in, the noise > seems more 'patterned' on the HSV-blended version (shows some kinds of > structure, patches, homogeneous areas with more defined, thicker > borders). > > > The better noise characteristic you mention (better on DSC_8834.jpg > than on DSC_8834_01.jpg) seems pretty clear to me. > > From my experience, the pattern you mention have similar size as > typical *color* noise patterns in photographs. > > I'm not a human vision specialist yet have some past experience during > my Ph.D. in robotic vision where the colorspace used for computation > has sometimes important impact on the effectiveness/robustness of some > algorithms. > > In the case of your observation, I would guess it is related to the > fact that performing image operations on HSV colorspace misfits/mixes > what human vision perceives as luma and chroma. As a consequence, the > noise reduction performed on S and V "bleeds" into what the eye > perceive as luminance, where it appears as the patterned noise you > mention. This theory goes in the same direction as your observation. > > For more information, read the paragraphs above and below the turtle > photographs on https://en.wikipedia.org/wiki/HSL_and_HSV#Disadvantages > > Can anyone elaborate the difference between "color" and "chroma" > blending mode in this respect ? This may have been pointed out already, but https://github.com/darktable-org/darktable/blob/master/src/develop/blend.c#L2035-L2036 _blend_color(): color blend; blend hue and chroma, but not lightness - blend hue along shortest distance on color circle
https://github.com/darktable-org/darktable/blob/master/src/develop/blend.c#L1898-L1899 _blend_chroma(): chroma blend - just blends C channel in LCH (for Lab based iops), or S channel in HSL (for RGB based iops) > Regards, > > -- > Stéphane Gourichon Roman. > ------------------------------------------------------------------------------ > > _______________________________________________ > Darktable-users mailing list > darktable-us...@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/darktable-users > > On 3 November 2016 at 16:18, Roman Lebedev <lebedev...@gmail.com> wrote: >> On Thu, Nov 3, 2016 at 5:57 PM, Andy <t3k...@gmail.com> wrote: >>> Hi all. >>> I'm new to darktable and somewhat new to raw image processing so please >>> excuse me if this is a naive question. >>> I was trying to denoise some images from my Sony a7 II R shot at 51200 ISO. >>> I followed some tutorials that recommended applying wavelet denoise with >>> blend=color and non-local means with blend=lightness. >> Also do try blend=hsv color and blend=hsv lightness. >> >>> I noticed some bright green highlights appearing. I played around with the >>> demosaic-ing and noticed that it even happened with >>> the "rough monochrome" demoisaicing and so I thought it might be worth >>> asking if this is a bug or some odd interaction of the filters. >>> You can find a picture here: >>> https://whttps://www.dropbox.com/s/ozjy3dk84zgvs6s/DSC00961.ARW?dl=0 and the >>> xmp here: ww.dropbox.com/s/fr24nz7zgz7xgd9/DSC00961.ARW.xmp?dl=0 >>> >>> If you go to the highest zoom level with wavelet denoising on the color and >> >>> raw monochrome demosaic, you will see the bright green artifacts. >> Monochrome demosaic is NOT meant to be used to "monochromly" demosaic >> the normal raw files. It is only meant to be used for the raw files from >> cameras >> with color filter array physically removed, scraped off. >> >>> They disappear when disabling the color denoising with wavelets. >> The profiled denoise is tuned to the properly-demosaiced image. >> If it does exhibit some artifacts when used on non-demosaiced input >> (because that is basically what monochrome demosaic does), >> i would not be surprised. >> Because monochrome is, as far i'm concerned, the exact opposite of color. >> >>> Using any other demosaic algorithm, you'll see magenta artifacts in the >>> highlights as soon as you turn the color denoising on. >> >>> My question is: is this expected? In particular with the monochrome demosaic >>> the artifacts seem very odd. >> I'd *personally* say yes. >> >>> But in general >>> I'd love to get rid of the bright green / magenta artefacts in the >>> highlights when doing the color denoise. >>> >>> Thank you! >>> >>> Andy >> Roman. >> >>> ____________________________________________________________________________ >>> darktable user mailing list >>> to unsubscribe send a mail to darktable-user+unsubscr...@lists.darktable.org >>> >> ____________________________________________________________________________ >> darktable user mailing list >> to unsubscribe send a mail to darktable-user+unsubscr...@lists.darktable.org >> ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to darktable-user+unsubscr...@lists.darktable.org
