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Problem with FFT - Strange Behavior

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  #1  
Old 09-15-2006, 11:28 PM
rnbluvva's Avatar
rnbluvva rnbluvva is offline
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Problem with FFT - Strange Behavior

Hi everyone!

How ya doing?

I have an image with a serious red color cast. I took the color cast out and noticed that there is a bumpy paper texture. So I went ahead and followed byRo's FFT tutorial to eliminate the honeycombs. I've run into a weird issue where I see the strangest thing in my channels when I go to clean up the 'stars'. The Red channel is completely black. The green channel is grey with no stars and the blue channel is completely gray.

I thought this might have something to do with me taking the red color cast out of the image. So I went back to the original layer and tried the FFT on it. Same thing happens.

So just for the heck of it, I went throught the process of doing IFFT to see what would happen. My whole image turns a really pretty shade of blue! LOL

Why are my FFT'd blue and red channels solid colors? Why isn't FFT working on this image?

Anyone know a fix or another way for me to get rid of the honeycomb texture without totally loosing all the detail in my image?

Thanks,
Nat
Attached Images
File Type: jpg hcomb-family-portrait.jpg (96.9 KB, 49 views)
File Type: jpg family-portrait.jpg (96.6 KB, 41 views)
File Type: jpg fft-weirdness.jpg (99.2 KB, 27 views)
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  #2  
Old 09-16-2006, 12:04 AM
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mistermonday mistermonday is offline
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Hi Nat, I ran your 1st image through Image Analyzer which I prefer to use (and it is free). The pattern was very easily defined and was very easily removed. Also note that the pattern is not too pronounced and you will find that a noise filter like Noise Ninja will eliminate the pattern much more quickly for this image.
Regards, Murray
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File Type: jpg RNBLUVVA hcomb-family-portrait rev MM.jpg (85.4 KB, 34 views)
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  #3  
Old 09-16-2006, 12:23 AM
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Craig Walters Craig Walters is offline
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hi natalie,

ignore the blue and green channels. it's the red that shld have the stars. are you using FFT or RGB FFT? i used rgb fft and got nice stars in the red. the sequence i used is:

duplicated to a new layer.

ran rgb fft on the duped layer.

split channels to rgb.

clone out the stars (i use clone instead of black paint, though not sure yet if it works any better than black)

re-combine the channels.

run IFFT RGB

done.

here's a copy of my red channel after fft rgb.

craig
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File Type: jpg Red2-1-k-1.jpg (95.9 KB, 18 views)
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  #4  
Old 09-16-2006, 12:30 AM
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Craig Walters Craig Walters is offline
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and here's a copy of the finished fft process, including re-combining with the original and setting the layer to luminance.

craig
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Old 09-16-2006, 02:28 AM
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Flora Flora is offline
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Hi Nat!!

..always nice to see you!!!

about your FFT problem ...
Quote:
Originally Posted by rnbluvva
The Red channel is completely black.
... Alex Chirokov's FFT plug-in seems to have to have 'limits' with size/resolution of the image ... (don't know if other FFT filters/programs have it too...) ... meaning when 'passing' that limit, it starts behaving exactly as you explained ...

You will find some answers here, here and here ....

Hope this helps...

Take care.
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  #6  
Old 09-16-2006, 06:55 AM
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rnbluvva rnbluvva is offline
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Talking File Was Too Big!

Hi all!

Nice to be back for a bit!

I think the size is the issue here. It's a huge image of 600dpi and an 8x10. From what I read in the links Flora left, this must be my problem! No worries tho, I will work around it.

Murray- Thank you for the tips on Image Analyzer and Noise Ninja. I will get those and try them.

Craig- hiya! Thanks for running the FFT. I had run RGB FFT, but as I mentioned above, the size must be the issue as I see it worked perfectly for you!

Flora- wonderful to see you as well. I hope you are well and that you haven't been anywhere with many internet blackouts lately! I really appreciate you leaving those links as it solved my mystery. Serves me right for not doing a proper enough search! Sorry about that!


Thanks so much to everyone who responded. I will post up my final when I am all done!

Nat
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  #7  
Old 09-16-2006, 08:50 AM
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Daviskw Daviskw is offline
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Hi There

I guess it is nice to have a FFT plug-in but to me the Image Analyzer is easier to use. No expert but it does seem to do a good job most times.

Butch
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  #8  
Old 09-16-2006, 11:46 PM
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Craig Walters Craig Walters is offline
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hi natalie good to see you home again. hope your music is going well. hope you're taking tons of pictures on all your travels. post some up sometime

here's a thought; if this is a size thing that's causing the problem, try cutting the size in half, run fft rgb, then increase the size and do the luminance blend mode afterwards. you might lose a tiny bit of detail, but it might get you by the problem.

also, butch is right about image analyzer. it's a good program. i just havent put it back on my new machine yet but i had it before and liked it.

craig
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