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 <[email protected]> Date: 12 September 2015 at 09:19 Subject: Re: [Darktable-users] profiled denoise - colour vs HSV colour To: [email protected] 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 ? Regards, -- Stéphane Gourichon ------------------------------------------------------------------------------ _______________________________________________ Darktable-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/darktable-users On 3 November 2016 at 16:18, Roman Lebedev <[email protected]> wrote: > On Thu, Nov 3, 2016 at 5:57 PM, Andy <[email protected]> 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 [email protected] >> > ____________________________________________________________________________ > darktable user mailing list > to unsubscribe send a mail to [email protected] > ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to [email protected]
