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Using the FFT filter to remove photgraphic paper texture

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  #71  
Old 12-19-2005, 12:17 PM
Bmud Bmud is offline
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Cool !!! Secrets of Key Star Finding !!!

Guess what. Let's say you're like me and you just scanned a 1x2 inch image at 1200dpi and the moire/patterns are ridiculous. After the FFTRGB filter there are too many stars to count, and the significant patterns are difficult to pick up. Good news. There's a handy guide right under your nose to finding the right stars, the "Key Stars" as I call 'em.

Look at your green channel at 50% zoom.

We've been talking a lot about the red channel but not much about the green one. Turns out that dropping a black star where you see a "cup lid straw hole" is right where you need to be. Use you imagination and discretion to figure out if you need to repeat those stars out further by eyeballing the distance to the main star's center or cardinal axis depending on the behavior of your pattern.

Just stay away from putting black on either axis of the main star without being really accurate with your clicking -- it's what creates that crazy black smoke.

By the way, if you're using my star brush make sure that the Flow is set to 100%. I think I have it saved in the preset as 50% which will mess things up. I'd appreciate if someone let me know if it's OK straight out of the cereal box.
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Last edited by Bmud; 12-22-2005 at 10:17 AM.
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  #72  
Old 12-19-2005, 01:46 PM
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Cameraken Cameraken is offline
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Hi Bmud.

I could be wrong here but I don’t think you can save the brush opacity or Flow. When I load your FFT brush the opacity stays as it was previously set. I think this happens with all brushes so I don’t think you can save the Opacity/Flow.

Some interesting ideas there could you post an example of a "cup lid straw hole"

By the way, have you seen this thread?
http://www.retouchpro.com/forums/sho...g+stripes+ugly

There are only 2 stars but they are on the axis. I guess that’s what you mean by Black Smoke.


Ken

Last edited by Cameraken; 12-19-2005 at 07:20 PM.
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  #73  
Old 12-22-2005, 09:48 AM
Bmud Bmud is offline
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This post is just to let you know that I've recieved everyone's comments about my posts being hard to follow. I'm spell checking and revising and attaching screenshots riiiiight nooow.
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  #74  
Old 12-23-2005, 07:09 PM
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bart_hickman bart_hickman is offline
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Important that texture be vertical/horizontal

This might have been mentioned before, but in the interest of completeness, I thought I would mention that making sure the texture aligns perfectly in the horizontal/vertical directions will simplify the spur pattern and thus improve the final result. That means if you have texture pattern that is somehow at an angle with respect to the photo, it will ease the job if you either rotate the photo in the scanner or rotate it in Paintshop/Photoshop prior to doing the Fourier transform.

I've occasionally seen texture that was slightly non-linear. In that case, see if you can warp the photo to make the pattern as linear as possible prior to the FFT. Then remove the spurs. Then undo the warping on the cleaned photo. If the warping is too severe, then the trick of scanning twice at 0 and 180 degrees might be to only option.

Bart
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  #75  
Old 12-24-2005, 06:30 PM
Taco Taco is offline
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I've searched for a while for something that would remove the moire (or halftone dot) pattern that is found in magazine prints. I think this has a lot of potential. One complaint that I have is that it's not able to handle a 600 dpi scanned image (at least not a full page). Another is the added "noise" that comes with it. I've been considering buying one of the commercial versions, but can anyone tell me if it can handle larger images?

I think a giant leap forward would be if it were automated. Sure, there's a script, but that is only part of it. I'd like to apply filter and process complete. I wouldn't hesitate to pay for a commercial version if this were the case.

Nice site, and thanks for the help.
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  #76  
Old 12-27-2005, 08:35 PM
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bart_hickman bart_hickman is offline
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Median filter and NR tool

Seems like just using the median filter (bare minimum needed to soften the pattern), followed by a good NR tool (Neat Image, Paintshop Pro, etc...) seems to work pretty well for that. Sometimes those magazine patterns are very irregular--the FFT will have a ton of harmonics and thus be time-consuming.

Bart
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  #77  
Old 12-28-2005, 11:43 AM
Bmud Bmud is offline
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I found today that FFT really is just fine the original way we were doing it with the FFT and median filter. I split a 600dpi image up today and did the CMYK channels seperately only to find that it comes out more harsh and messes up the colors -- so I had to use a median layer to correct color anyway.

Maybe the trick to getting color halftone removal to look better is redesigning a brush with a linear gradient to help with the circles of different sizes.

I agree though. this i all very fascinating, but I'm about fed up with the work involved. A full blown pattern removal filter would be nice.

If this discussion got any more technical we'd have enough to figure it out ourselves :P
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  #78  
Old 01-02-2006, 11:26 AM
Taco Taco is offline
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Quote:
Originally Posted by bart_hickman
Seems like just using the median filter (bare minimum needed to soften the pattern), followed by a good NR tool (Neat Image, Paintshop Pro, etc...) seems to work pretty well for that. Sometimes those magazine patterns are very irregular--the FFT will have a ton of harmonics and thus be time-consuming.

Bart
I've been doing the median filter/noise reduction for a while and it's pretty good. As well as scanning at 600 dpi and reducing to 300 dpi. but I'm always on the look out for something better.
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  #79  
Old 01-03-2006, 01:08 PM
Bmud Bmud is offline
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More recently, with pictures that are big enough, I've just been running the despeckle filter to kill halftone patterns.
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  #80  
Old 01-04-2006, 08:45 PM
Taco Taco is offline
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not a big fan of despeckle myself, but the new noise reduction filter in psp X has a lot of potential. A friend of mine swears by it to remove the regular pattern without harming the detail. I can't match the results yet unfortunately, but I'm still playing around with it.

Anyway, didn't mean to get this subject off topic. I'm still interested in an automated fft filter such as this. I set up a script is psp that uses the poster filter (set to 4) and then the threshold filter (set to 152) to seperate the brighter stars from the darker background. cut out the center, then color it gray, overlay it to a copy of the fft image and use ifft. the results work and are pretty quick, but it could be very much improved. I left out a lot of details, but it was just something I was toying with.
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