Author Topic: Noise Reduction Options Clarification  (Read 3245 times)

Offline jerryyyyy

  • PixInsight Old Hand
  • ****
  • Posts: 425
    • Astrobin Images
Noise Reduction Options Clarification
« on: 2013 June 02 10:15:07 »
Looks to me like there are three maybe four main noise reduction processes:

AdaptiveContrast-Driven Noise Reduction (ACDNR)
AtrousWavelet Transform (AKA AtrousWavelet Noise Reduction? in the past)
TGV Denoise
Possibly also Deconvolution would be considered Noise Reduction.

Now, seems like you do not want to use them all since that would likely introduce more error than it would remove.  So maybe best to prioritize one for the linear phase and one for the non-linear phase....

If I understand correctly AtrousWavelet Transform should be used on the linear image, as is Deconvolution.

The ACDNR or TGV Denois should be used on the non-linear images.  Advantages/disadvantages?

In the ballpark here?
Takahashi 180ED
Astrophysics Mach1
SBIG STT-8300M and Nikon D800
PixInsight Maxim DL 6 CCDComander TheSkyX FocusMax

Offline Carlos Milovic

  • PTeam Member
  • PixInsight Jedi Master
  • ******
  • Posts: 2172
  • Join the dark side... we have cookies
    • http://www.astrophoto.cl
Re: Noise Reduction Options Clarification
« Reply #1 on: 2013 June 02 13:53:10 »
Hi Jerry

First a clarification. Yes, deconvolution "might" be used as a noise reduction tool, but it has not been designed with that in mind. Deconvolution procedures, apart from a naive filter inversion, includes what is called a "regularizator". The goal of these "objects" (or algorithms) is to prevent noise amplification in the procedure of recovering the true signal at high frequencies (or small scales). In the most simple regularizators, this means just to blur the image a little bit, and in most advanced ones some prior knowledge is used, like the image should be smooth with some sharp edges, or that the image is mostly black with a few bright dots.
So, the bottom line is that even when deconvolutions may be used as noise reduction algorithms (and we are implementing a new deconvolution also based in the total generalized variation), they are not recomended for this task. Even when they noise reduction algorithm share the same regularizator (as will be the case of tgvdenoise and tgvrestoration), noise reduction algorithm are optimized for this task, and include some ad-hoc routines to enhance the performance.

Now, about noise reduction algorithm guidelines... In my opinion TGVDenoise seems to be the better choise in most cases, for linear or non-linear data. The algorithm assumes that there is gaussian, homogeneus noise in the image, but with our local support implementation there is an extra flexibility that allows the algorithm to work quite well in presence of poisson noise, and other structurated noises.
If the image contains clearly distinguisable noise patterns, sinosoidal specially, then noise reduction in the fourier space is recommended. For that, I wrote a module called NotchFilter, similar to the DefectMap process, that works specially well. Also the TGVRestoration process could be used, in the fourier map mode that I'm including.
For pepper and salt noise, other non-linear filters like a median filter are more better suited.

And that's it, in a nutshell. There is still room for ATWT and MMT, specially with linear data or weird noise, but ACDNR is basically replaced by TGVDenoise. Also I won't take out SCNR, specially to fix color casts after noise reduction with other algorithms.
Regards,

Carlos Milovic F.
--------------------------------
PixInsight Project Developer
http://www.pixinsight.com

Offline jerryyyyy

  • PixInsight Old Hand
  • ****
  • Posts: 425
    • Astrobin Images
Re: Noise Reduction Options Clarification
« Reply #2 on: 2013 June 02 14:54:36 »
Thanks, thus for a novice confused in the supermarket of noise filter choices, it would probably be best to focus on the new TGVDenoise (TGVD) as the main player in denoising. 

Seems that for me that TGVD should be used after The RGC combination, Crop, DBE, ColorCalibration and the STF/HT stretch,  but probably before masked curves.  SCNR would be a last correction for green primarily. 

If I use Deconvolution, probably should be on just a Luminosity component, separate from the RGB.  If you add in an L component, would you denoise that separately before combining with RGB, or do them together after combination?

Devil in in the details >:D
Takahashi 180ED
Astrophysics Mach1
SBIG STT-8300M and Nikon D800
PixInsight Maxim DL 6 CCDComander TheSkyX FocusMax