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FFT problem. Some idea?

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  #1  
Old 01-03-2011, 12:51 PM
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Florin Florin is offline
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FFT problem. Some idea?

Hi everybody. I have again one of these damaged picture to retouch. It has a global texture which must be removed so I used very carefuly the FFT filter, like always I'm doing. However, the final resoult still presents some horizontal line patterns as you can see in the attached sample. I did this 3 times again but the lines are always there.
I've upload the high resolution file in this server:
http://www.mediafire.com/i/?3eux60y21b3hati
Maybe someone could give me a hand to solve this.
PS "File not found" is fake. You can download it.
Regards and thank you
Attached Images
File Type: jpg After_FFT.jpg (83.3 KB, 102 views)
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Old 01-03-2011, 03:37 PM
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Re: FFT problem. Some idea?

I see where you painted out the pattern.

The rest of your pattern is located almost along the vertical band in the FFT Power Spectrum. You have to block out THOSE frequencies, too.

The danger is that the rest of your horizontal lines in the image will also go away.

Can't find your original, high-quality image.
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File Type: jpg sans-hline.jpg (49.5 KB, 53 views)
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Old 01-03-2011, 04:12 PM
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Florin Florin is offline
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Re: FFT problem. Some idea?

Thank you for answer.
Open the link http://www.mediafire.com/i/?3eux60y21b3hati and clic above, over "Download this image"
So, you say "You have to block out THOSE frequencies, too..." How should I do this? I used the FFT several times and had no resoult, the lines are still there..
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Old 01-03-2011, 05:50 PM
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Tony W Tony W is offline
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Re: FFT problem. Some idea?

Hi Florin
I am not at all sure if this is of any help but the image link you posted is a grayscale version.

I have tried with my version of FFT without any success even tried convert to RGB - I was going to try rotating the image and overlaying etc. I think that FFT needs therefore an RGB image to start with.
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Old 01-03-2011, 06:31 PM
unimatrix001 unimatrix001 is offline
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Re: FFT problem. Some idea?

FFT does require an rgb image to start with. it uses the red channel to remove the texture.
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Old 01-03-2011, 07:14 PM
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Florin Florin is offline
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Re: FFT problem. Some idea?

Hi, thank you my friends.
Yes, I've upload it as grey because is "lighter" than RGB. Just convert the mode from grey to rgb.
I always use the green channel for the FFT, should I try with the red one?
I'll make a try now.
I must confess that I was doing this kind of retouch before (to be a member here) painting the image, every single pixel, but it's a damn job. Takes a lot of time. Last year, in ReouchPro I learned about this filter and I'm really saving a lot of working time whenever people are sending me these textured pictures. This is the first time it did not work well.
Cheers
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Old 01-04-2011, 08:33 AM
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Florin Florin is offline
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Re: FFT problem. Some idea?

Well, I made a try inverting the image after the first FFT pass (invert + FFT again + re-invert) but the resoult it's not so attractive. The lines went away but the picture is too blurry.
I belive this will be done with manually removing these lines.
Cheers
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Old 01-04-2011, 09:09 AM
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Re: FFT problem. Some idea?

Here is the image (JPEG, quality = 95 to stay under the 100KB limit) with the pattern removed.

Also attached is the mask I used to do it. (scaled up to 1024x1024)

Used my software (FoveaPro) because I wanted to see the problem.

If you look at the mask in a vertical line down the center are a number of dots -- those dots represent the frequencies you were unable to remove when you did it by hand, above.
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File Type: jpg fft-pattern-removed.jpg (98.7 KB, 81 views)
File Type: png Frequency-Mask.png (23.2 KB, 56 views)
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Old 01-04-2011, 09:12 AM
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Re: FFT problem. Some idea?

Another thing you can try if you're willing to rescan the image is to rotate it by about 15° so that none of the pattern falls on a horizontal or vertical line. That trick (rotate the image a little and try again) should be in your repertoire.

The problem here was that you could not distinguish the pattern from the power spectrum + cross shape to identify H & V frequencies that needed to be removed.
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Old 01-04-2011, 09:14 AM
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Re: FFT problem. Some idea?

Very nice, JCR, much better than the FFT pass. Thank you
How could I get this mask/filter please?
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