Author Topic: Background noise reduction  (Read 46458 times)

Offline Enzo De Bernardini

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Re: Background noise reduction
« Reply #15 on: 2011 June 29 08:13:59 »
I really like this kinds of examples. Thanks Juan!

(humm...tagged bookmarks to external links inside PI doc browser? ;) )

Enzo.

Offline Juan Conejero

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Re: Background noise reduction
« Reply #16 on: 2011 June 29 09:34:36 »
Hi Robert,

thanks juan. we've seen several methods for background noise reduction: acdnr, wavelets and greycstoration. is there a rule of thumb for which one is applicable to what situation?

Just as a rule of thumb —which means that you can always find examples where this is not applicable:

GREYCstoration is an extremely powerful noise reduction tool (perhaps the best one IMO) for daylight images. For deep sky astrophotography it works well during the final stages of post processing, as a finishing tool to be applied cautiously, but I don't recommend using it otherwise. When applying it, watch for possible artifacts generated as a result of excessive anisotropic filter response. This algorithm (at least in its present implementation) doesn't work for linear data.

ACDNR has been our noise reduction workhorse for a long time. When properly applied, ACDNR yields excellent results for nonlinear deep sky images. However, there are many cases where applying it correctly isn't an easy or obvious task. This happens when the noise must be reduced at a wide range of dimensional scales. In these cases, several applications are necessary with increasing filter size and mask protection. This can lead to manual procedures requiring a lot of experience and trial error work.

I designed the current version of the ACDNR algorithm in 2005-2006. I think it's time for a serious revamping. New noise reduction tools are now necessary, with more efficient algorithms and implementations. So don't be surprised if ACDNR gets moved to the Obsolete category in a future release, in the short-medium term, and replaced with new, more efficient noise reduction tools.

Finally, we have ATrousWaveletTransform. I've just put a good example of what this tool can do for noise reduction. As usual, the multiscale paradigm provides new and powerful ways of facing old problems. In this case, noise reduction becomes simplified because wavelet layers allow us to isolate the noise at different dimensional scales in a natural way. With just two or three simple and easy-to-understand parameters we can attack the noise very efficiently, with the added bonus that it works equally well on linear and nonlinear data. I recommend trying wavelet-based noise reduction in the first place for deep sky images. When no good results can be achieved with wavelets —no algorithm or tool works in all situations—, ACDNR remains as a solid fallback option.
Juan Conejero
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Offline Harry page

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Re: Background noise reduction
« Reply #17 on: 2011 June 29 11:07:43 »
Hi Juan

Thanks for your Demo , I need to take it all in and as my brain is small I will need a few days  ;D

I do have some binned RGB but it seems to be very poor as I am new to this Binned thing , plus I had some hardware issues to resolve  :'(  my efforts so far are not satisfactory and My RGB might even be beyond your repair  :footinmouth:

Regards Harry
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Offline zvrastil

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Re: Background noise reduction
« Reply #18 on: 2011 June 29 12:37:22 »
Hi Juan,

thanks a lot for demo, it is excellent. I wonder how many hidden (= undocumented) pearls like this one are there in the PixInsight  8)). I've noticed this noise reduction parameters in ATWT some time before, but I did not experimented with it not knowing what I could expect. I'll definitely start to now.
One question - would it be possible to compute these parameters from "noise sample" - small preview containing only noise? Maybe some kind of script doing this could highly improve ease-of-use of this method.

regards, Zbynek

Offline georg.viehoever

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Re: Background noise reduction
« Reply #19 on: 2011 June 29 13:09:17 »
...hidden (= undocumented) pearls ...
>:D
Georg (6 inch Newton, unmodified Canon EOS40D+80D, unguided EQ5 mount)

Offline zvrastil

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Re: Background noise reduction
« Reply #20 on: 2011 June 29 23:19:08 »
I recommend trying wavelet-based noise reduction in the first place for deep sky images.

Maybe, it's good idea to add ATWT to NoiseReduction category then...

Offline Jordi Gallego

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Re: Background noise reduction
« Reply #21 on: 2011 June 30 11:40:27 »
Thanks for the example on ATW noise reduction Juan  ;)

I started to use this NR tool after you first presented it to us (with release 1.5). I was really impresed by the result on the example you showed us there:

http://pixinsight.com/forum/index.php?topic=1105.0

it is really a very nice and useful (and maybe not so hidden :D) NR tool!

Regards
Jordi
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Offline Juan Conejero

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Re: Background noise reduction
« Reply #22 on: 2011 June 30 12:39:26 »
Hi jordi,

Quote
I started to use this NR tool after you first presented it to us (with release 1.5).

it's been two years since that post... and it seems yesterday!  :P
Juan Conejero
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Offline Harry page

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Re: Background noise reduction
« Reply #23 on: 2011 June 30 12:41:45 »
Hi

Ok digested the info  O:)    I feel a video coming on  ;)

Harry
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Offline Juan Conejero

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Re: Background noise reduction
« Reply #24 on: 2011 June 30 12:51:36 »
Let it come to us!  O0
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Offline h0ughy

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Re: Background noise reduction
« Reply #25 on: 2011 June 30 21:04:44 »
looking forward to this Harry, this is good stuff.
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Offline Nocturnal

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Re: Background noise reduction
« Reply #26 on: 2011 July 06 20:59:58 »
I've restricted NR to small scale because of the lumpyness that occurs with large scale ACDNR. I'll give this thread a good read next time I'm working on an image. Need capture some data first.
Best,

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Offline gvanhau

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Re: Background noise reduction
« Reply #27 on: 2011 July 07 15:23:53 »
For those of us who are relatively new to PI  this was still  a hidden treasure .
Thanks Juan for rediscovering it for us. :D

I'll give if a try this evening.

regards
Geert
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Offline Philippe B.

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Re: Background noise reduction
« Reply #28 on: 2011 July 08 00:28:07 »
Hi
On ATWT, I saw k-sigma noise thresholding could be better than NR on 3-4 first layers
I get also a nice result on ACDNR with a 8-10 in Std-Dev value and many other custom values and a strong mask.

Thanks Juan for this tutorial. It helps to discover each day more and more PI features we didn't realize they were there  ;)

Offline Josh Lake

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Re: Background noise reduction
« Reply #29 on: 2012 January 16 16:42:05 »
Now the image is no nice and seems to respond so well to everything I do, that I can't resist doing a more elaborate example. This is a first nonlinear stretch. As is customary in PixInsight, we have high precision tools so this can be done perfectly in a single step --forget all that ugly multiple stretches so common in other applications. They simply reflect the inability of those applications to handle real image data (they are image retouching toys, not real image processing software).

Wow, Juan, you nailed it! You make your case convincingly, and as I've been 'evangelizing' on Reddit about PixInsight (under user PixInsightFTW), I'm often asked to compare other imaging software. I think 'image retouching toys' vs. 'real image processing software' will be a new catch phrase for me.

Question: I've been following Vicent's workflow these days for getting through linear and non-linear data. Where would you recommend that linear AtrousWavelet noise reduction take place? After color calibration and just before Histogram Transformation?