Author Topic: Image of noise  (Read 2144 times)

Offline CharlesW

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Image of noise
« on: 2013 December 04 17:40:53 »
Forgive me if this is already possible and if not, a wish list item. I'm a newb and still learning what noise looks like. With ABE and DBE you end up with an image of the gradients that were removed. Can an image of the noise that is removed with ACDNR/TGVDenoise etc. be generated? If any structure to the noise starts showing up, you might assume you've gone too far.

Offline mschuster

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Re: Image of noise
« Reply #1 on: 2013 December 04 18:54:43 »
I use a PixelMath expression like "A - B + 0.5" with the rescale option disabled, i.e. just the difference between the noisy input and the denoised output, the 0.5 is added to avoid clipping. Apply an STF to see the result.

The result is "Method noise", i.e. the noise guessed by the denoising method.

Ideally method noise should have the same statistics as the noise. But don't interpret this to mean that method noise should show no structure. Since noise in CCD/CMOS images is highly intensity dependent due to shot noise, the method noise of a perfect denoising will of course show this structure.

Nonlinear processing affects noise statistics, which may make method noise harder to interpret.

Regards,
Mike


Here is an example on linear data. Input is a calibrated sub, stretched to make it visible:



Here is the output, stretched likewise:



Here is the method noise, also stretched. Structure partially due to intensity varying noise, and partially due to not guessing perfectly. The cosmic ray hits are not removed, as the method does not consider them to be noise. The STF used to view method noise can also affect your judgement of structure.



« Last Edit: 2013 December 05 09:22:03 by mschuster »

Offline GJL

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Re: Image of noise
« Reply #2 on: 2013 December 04 23:54:03 »
Hello Mike,

you`ve forgotten to add the pictures.

Gerhard

Offline CharlesW

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Re: Image of noise
« Reply #3 on: 2013 December 05 06:22:27 »
Thank you, exactly on point.

Charles

Offline NGC7789

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Re: Image of noise
« Reply #4 on: 2013 December 05 06:30:47 »
I saw the pictures at home, but here at work I do not. Both on Firefox. Interesting.

Online pfile

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Re: Image of noise
« Reply #5 on: 2013 December 05 08:56:11 »
they are showing up in safari on osx here at home. they are in tif format and hosted on an external site which may be blocked by a work firewall…?

rob

Offline georg.viehoever

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Re: Image of noise
« Reply #6 on: 2013 December 05 09:05:50 »
Georg (6 inch Newton, unmodified Canon EOS40D+80D, unguided EQ5 mount)

Offline mschuster

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Re: Image of noise
« Reply #7 on: 2013 December 05 09:23:51 »
The images are .png now. Sorry for the trouble.

Mike