Digital Camera Noise Removal: Experience of GREYCstoration? Any good hints?

jarvist

jarvist

New member
GREYCstoration is a badly named but sophisticated method of removing noise from digital camera shots:
http://cimg.sourceforge.net/greycstoration/

Its free + opensource, with plugins for GIMP & GUI versions for windows etc.

It seems that you need fairly exacting 'recipes' to remove the noise but not destroy the detail, and I was wondering whether anyone has fiddled for this with caving shots, and how far they got?

And are there any other black-magic tricks for noise removal?
Previosuly all I've ever really done was Gaussian Blur to smooth noise, then fiddled with levels + dodged/burned (generally with the 'highlights' choice in gimp).

I've also read of amateur astronomers taking a 'dark' photo for the same exposure as the real one, and then deducting it directly from the genuine shot (pixel by pixel) to get rid of some noise. Has anyone tried this? And if so, does one need to take the 'dark' shot at the same time as the exposure (same sensor temperature, temperament, phase of moon, etc.), or can one tabulate a whole set of different exposures at home? And how much does the noise fluctuate in both the short and the long term? And do digital cameras now-adays already try and do this kind of trickery by themself?
I believe that digital camera 'long exposures' are actually multiple short exposures when are then composed together by the digital camera (including a deconvolution of the expected sensor noise?)...

I've only tried a couple of photos with GREYCstoration so far, but here they are along with settings used for anyone who's interested:

Gaping Gill Main chamber, 15s exposure with (mainly) ambient light from above, Canon A520.

-alpha 1.6 -p 1.2  -dt 100

Orig (Click on photos to see full res):
http://www.union.ic.ac.uk/rcc/caving/photo_archive/trips/2008-04-25%20-%20avalanche2/GG_mainchamb_orig.html
Restored:
http://www.union.ic.ac.uk/rcc/caving/photo_archive/trips/2008-04-25%20-%20avalanche2/GG_mainchamb_GREYCstoration_a16_p12_dt100_gimp_burn.html

Orig:
http://www.union.ic.ac.uk/rcc/caving/photo_archive/trips/2008-04-25%20-%20avalanche2/GG_mainchamb2_orig.html
Restored:
http://www.union.ic.ac.uk/rcc/caving/photo_archive/trips/2008-04-25%20-%20avalanche2/GG_mainchamb2_GREYCstoration_a16_p12_dt100_gimp_burn.html

And for a flash photo with lower noise; Avalanche Inlet, flash is Vivtar 283 on Firefly, Canon A520 200ASA(?) 1/60s

-alpha 1.6 -p 1.2  -dt 50

Orig:
http://www.union.ic.ac.uk/rcc/caving/photo_archive/trips/2008-04-25%20-%20avalanche2/Avalanche_orig.html
Restored:
http://www.union.ic.ac.uk/rcc/caving/photo_archive/trips/2008-04-25%20-%20avalanche2/Avalanche_GREYCstoration_a16_p12_dt50_gimp_burn.html

Other photos from that trip:
http://www.union.ic.ac.uk/rcc/caving/photo_archive/trips/2008-04-25%20-%20avalanche2/
 
I've not tried using any noise reduction techniques (through lack of time, not lack of need!). But having read about commercial applications to do this, they do recommend profiling the noise from your camera. This should be done at least for each ISO setting, as this makes a significant difference to the noise levels in a picture. Purists may also profile for different ambient temperatures too. The profile is create by photographing a test card containing solid blocks of different colours. This shows up the different noise patterns in different colour areas and the software then tries to minimise similar patterns.

I believe noise reduction in cameras is subtracting a noise pattern taken from a black image away from the actual image. So that removes non-random noise (e.g. bright pixels due to sensor imperfections). The software techniques are trying to remove random noise patterns from the images.

If you record RAW images then this probably bypasses any in-camera noise reduction as it just captures the raw data from the camera sensor (please correct me if anyone knows otherwise).

That open source project looks very interesting. I had not come across it before. Looking at your example images if appears to do a pretty good job.
 
I occasionally use Neat Image as a plug in to Photoshop (although it also works as a stand alone).  It works very well,removing noise whilst maintaining detail and will profile cameras if necessary/profile from blank areas on the photo (i.e. areas of complete black/flat midtones etc).  It is quite cheap to buy (?25) and you can download trial versions.

Sadly I have no experience with the software you suggest.
 
It has to be said that by far the best way of dealing with digital camera noise is to reduce it in the first place, by resisting the temptation to crank up the ISO setting. I know that the digital age has been a boon for cave photographers, but just as in the old days of film there is no such thing as a free lunch - the higher the ISO the poorer the image quality. With film it was grain, contrast and colour fidelity that suffered when you used a fast film or push-processed, with digital you get noise. So while it's a pain to use bigger flashguns or bulbs underground instead of handy little 'uns, ultimately it's worth it if you are at all concerned with image quality. As has already been stated, shooting in RAW helps, as JPEG compression doesn't do image quality any favours.

Camera choice is important...I have a Canon Powershot that gives horribly noisy images at even ISO 200, and as a consequence I don't use it for much other than family snaps.

The best and quickest means I've found of reducing noise is as follows, in Photoshop:

1. Duplicate the layer
2. Apply Gaussian blur (Filter> Blur> Gaussian), while zoomed in on a dark or potentially noisy area. Don't overdo it.
3. Change the layer blend mode to 'Colour'.
4. Check carefully again, zoomed in, clicking the duplicate layer visibility icon on and off to compare, before flattening the image when you're happy.

This deals with most of the obvious coloured speckles in dark areas. I don't have experience of other software or plug-ins.
 
If looking at the before/after images without any hint as to what was meant to have been done, my thoughts would have been 'posterisation' or 'art effects' rather than 'noise reduction'.
 
I use Lightroom for pretty much everything - including noise reduction (separate sliders for limunance and colour). I have experimented with noise ninja and neat image in PS, but haven't used them enough to comment them. To reduce the amount of noise, it's important NOT to underexpose the photo and make it brighter afterwards. Use the histogram on your camera and expose as far to the right as you can without blowing the highlights. Also, I always shoot my pictures in RAW format, to give me as much data as possible to work on afterwards.

Here are a few examples of pictures shot in RAW and a single flash. All photos taken with a Nikon D80 @ ISO 400, f/5.6-8 and an SB600 flash.

http://www.arcticsilence.com/gallery/content/Mining/Sauda/dugnad-20.jpg
http://www.arcticsilence.com/gallery/content/Mining/Sauda/dugnad-19.jpg
http://www.arcticsilence.com/gallery/content/Mining/Sauda/dugnad-24.jpg
http://www.arcticsilence.com/gallery/content/Mining/Sauda/dugnad-26.jpg
http://www.arcticsilence.com/gallery/content/Mining/Sauda/dugnad-30.jpg
http://www.arcticsilence.com/gallery/content/Mining/Sauda/dugnad-33.jpg
http://www.arcticsilence.com/gallery/content/Mining/Sauda/dugnad-29.jpg

All images ? Francis Dougherty Paulin

Francis :)
 
Yeah, i've used noise ninja a couple of times too and it seems to work quite well (you can also select areas you do not want it to remove the noise from).

I was shown how to use it by a photographer who specialises in gigs. He swears by it.
 
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