Hi, I'd like to share my own experiences of dealing with extremely noisy images with darktable as well. For comparison I'm going to use the ARW image from this thread: https://discuss.pixls.us/t/playraw-high-iso-challenge/2778, since it's a rather difficult image to work with. I will be using AMaZE for demoasicing and Rec.2020 as the input color profile since it works much better than the default matrix of Sony A6000 in my experience. The applied-by-default base curves and sharpening modules are also disabled.
This is the RAW image with no denoising applied, to give an idea how bad the noises are in the photo: http://i.imgur.com/AgxvKby.jpg For reference this is denoised with RawTherapee with mode = lab, quality = high, luminance = 20, luminance detail = 10, automatic global chroma denoise, 3x3 median filter: http://i.imgur.com/hiXMklL.jpg RawTherapee eliminated nearly all chromatic noise and the luma noise left in the background are very fine and looks pretty non-obtrusive. It also preserves the details on the dog fur very nicely. The first attempt with darktable is using the recommended profiled denoise module in NLM mode on HSV lightness and another in Wavelet mode with HSV color at default strength: http://i.imgur.com/WGN5Y03.jpg This produces some blotches of luma noise in the background area which in my opinion is very distracting (which is further complicated by the fact that it brightens up the darker areas which makes it look worse). There are still larger patches of colorful noise visible and the details on the fur are almost completely wiped out. This another attempt using profile denoise. This time I switched to wavelet mode in the lightness instance with 50% blend to combat the blotchness, turned the strength of wavelet chromatic denoise to 4.0, and set color smoothing in AMaZE to 5 times: http://i.imgur.com/YaBAAJR.jpg This eliminates more noises while keeping a lot more details in the fur, but there are still some patterns visible in the background. The whole image also got a purple tint and at 100% view you can easily see some of those purple artifacts in the darker areas of image. The next is probably my go-to way of noise removal on high ISO images in darktable now. I used the equalizer's denoise preset with mix 2.0 and the lowpass module with radius=10 and lab color blending to apply a really strong chromatic denoise: http://i.imgur.com/wx0QGZN.jpg This looks a lot better even though some colorful patches are still visible in the darker areas, and the luma noise are now very similar to the result of RawTherapee. The downside is that it desaturates the image and smears the color (compare the red heart in the bottom-right corner, though it also removes the CA so I guess it isn't too bad :)). The processing is super fast compared to profiled denoise. This is another attempt, this time using the "denoise (bilateral filter)" instead of lowpass. http://i.imgur.com/I4WIvQy.jpg This wipes out all chromatic noise but also seems to wash out the photo and give it a slight purple tint. Finally, this is the result of aforementioned denoise_chinese dtstyle: http://i.imgur.com/NrQy3NV.jpg I guess the strength of noise removal of the style isn't high enough for this image. Overall I'd say RawTherapee's result is the best as it removes almost all chromatic noises without causing color casts or artifacts, and it produces very fine and non-obtrusive luma noise. Darktable with equalizer and lowpass modules comes close, but the other results look unacceptable to me. I really would like to know a way of noise removal that can rival RawTherapee since I like darktable's workflow more, so please let us know if you do discover one. :) PkmX ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to darktable-user+unsubscr...@lists.darktable.org
