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Forum: Digital Processing, Software, and Printing 05-13-2018, 05:03 AM  
Anyone using "selective Gaussian blur" for noise reduction?
Posted By BigMackCam
Replies: 10
Views: 1,616
Interesting - thanks for the info!


Now that I've got used to using the noise reduction features in Darktable's equalizer module, I'm very happy with it indeed - so I think that's what I'll be using from now on. But it's good to know there are other options for GIMP. Actually, I'm just playing around with G'MIC and the GIMP plug-in. I installed it for the film emulations, but there are some interesting noise reduction capabilities in that too :)
Forum: Digital Processing, Software, and Printing 05-12-2018, 02:59 PM  
Anyone using "selective Gaussian blur" for noise reduction?
Posted By BigMackCam
Replies: 10
Views: 1,616
Just a quick example of the results I'm finding possible with a combination of the equalizer and denoise (bilateral filter) modules...


This was a test shot I took some time ago with the K-5, at an extended ISO setting of 51,200. Processed in darktable for the first time today, and without a great deal of work. I'm sure I could improve on it. What impresses me is that the noise reduction has retained little details like the corrosion on the top of the guitar's machine head pillars. I'm impressed :)
Forum: Digital Processing, Software, and Printing 05-12-2018, 01:53 PM  
Anyone using "selective Gaussian blur" for noise reduction?
Posted By BigMackCam
Replies: 10
Views: 1,616
Thank you... I'll take a look at the Lowpass module. I wasn't even aware of that :o


Since my original post, I've been playing with the Equalizer module, and I'm getting the best NR results I've achieved so far with Darktable. Chroma noise isn't so well controlled with this tool (at least, not with very high ISO images) - but a combination of Equalizer and gentle denoise (bilateral filter) sorts that out. For luminance noise, it's awesome.



Per your comment, yes - I've found that a good demosaicing algorithm is essential in dealing with colour noise. I typically use VNG with five times colour smoothing. I understand it's quite process-intensive compared to PPG, but I'm running a fairly quick laptop (i7-4700MQ quad-core @ 2.4GHz, with 12GB of RAM and GeForce GT740M GPU), so it doesn't make a big difference for me.
Forum: Digital Processing, Software, and Printing 05-11-2018, 03:29 PM  
Anyone using "selective Gaussian blur" for noise reduction?
Posted By BigMackCam
Replies: 10
Views: 1,616
Thanks, Dave :)

I believe that's the purpose of the selective gaussian blur I'm trying out, rather than just a straight gaussian blur on the entire image. As I understand it, selective gaussian blur looks for areas of contrast below a user defined threshold and blurs only those areas.

The limitation I've already found is that if the image contains low contrast detail - such as fine detail on a flower petal - it's not always possible to find a threshold that keeps those details whilst blurring noise. Still, I'm finding it quite useful on higher ISO photos where the finer details are already compromised...
Forum: Digital Processing, Software, and Printing 05-11-2018, 02:04 PM  
Anyone using "selective Gaussian blur" for noise reduction?
Posted By BigMackCam
Replies: 10
Views: 1,616
Since my move away from Lightroom 6 on Win10 to Darktable on Linux Mint, there are very few things I miss so far, and lots of new things I like. But one of the areas I'm less impressed with is Darktable's luminance noise reduction... It's not bad at all, but doesn't produce the fine-grained results that Lightroom does, especially on high ISO files. Of course, that could very well be my lack of experience, but I've been playing with the various approaches quite extensively (including profiled denoise, which I'm really not keen on), and still haven't found one that works quite so well as Lightroom.

Anyway, today I came across an article on "selective Gaussian blur" for noise reduction, and found that GIMP - the image editor I'm using - has a filter for this, albeit with a very limited number of settings (I'm guessing, therefore, that commercial equivalents like Photoshop also have it?). I've been experimenting on a few ISO 1600 - 12,800 files from various cameras I own, and I'm really quite impressed by the results. It takes a while to apply the chosen level of selective blur to a full-size 24MP image, so it doesn't make for a fast workflow - but with careful adjustment, the end result is really rather impressive. I'm surprised at how much detail is retained, although admittedly I'm not one for heavy-handed noise reduction so my application of the filter has been relatively gentle.

So I'm wondering... who else here uses this technique for noise reduction, and what (I wonder) are the limitations? There's always a cost and/or limitations to these things... and I'd be interested to know if anyone has knowledge or advice they could impart.

Thanks in advance :)
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