Author Topic: Fourier transform - what to clone stamp  (Read 1946 times)

Offline cwiede

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Fourier transform - what to clone stamp
« on: 2014 August 26 09:07:25 »
Hi,
I have a solar H-alpha image, which shows a stripe-pattern in parts of the left half of the image. I don't know where it comes from, but I wanted to erase it with the Fourier transform tool. However I find it difficult to understand what to erase in the fourier transformed images (using clone stamp). Can anybody help me to understand the fourier transformed images better? As far as I know high frequency structures should correspond to pixels in the center, right? So the stripe-pattern should be somewhere far from the center. I attach the image and the fourier transformed images as jpg. You can download the original fit file here (7MB):
https://www.wuala.com/cwiede/public
Best regards
Christof Wiedemair

Offline oldwexi

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Re: Fourier transform - what to clone stamp
« Reply #1 on: 2014 August 26 13:08:01 »
Hi Christof!
Cannot recommend to use Clonestamp.
One Solution of many is to extract the stripes with MultiscaleMedianTransform Wavelet Layers.
Cooking recipe:
Rename Original Image to   "o"
drag over "o"  MultiscaleMedianTransform    8 Layers, Layer 6  -0.200,     Layer 7 -1.000,   Layer 8  -0.200
clone result, rename to "f"
PixelMath:   o-f     create new Image Name "diff"

This results in the wanted structure.
Stretch "diff" with STF -> Histo.
Use "diff" as Mask over "o" and
reduce with Curves the bright stripes in "o".

Gerald
Resulted Image at:
http://www.werbeagentur.org/oldwexi/gallery_deepsky/pixinsight_MMT.jpg


« Last Edit: 2014 August 26 13:15:37 by oldwexi »

Offline Carlos Milovic

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Re: Fourier transform - what to clone stamp
« Reply #2 on: 2014 August 26 14:04:31 »
I wouln'd recommend CS + Fourier either. These stripes have a medium frequency, so it is located close to the center of the fourier space. There, isolation of structures is more difficut, so is highly likelly that you'll end generating artifacts.
I liked a lot Gerald's multiscale suggestion.
Regards,

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

Offline cwiede

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Re: Fourier transform - what to clone stamp
« Reply #3 on: 2014 August 28 01:32:00 »
Hi Gerald,
works perfectly! Thank you very much! The mask protects more than just the stripes, but the result looks very good. I have to read more about this MultiscaleMedianTransform-Tool!
Best regards
Christof