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Using the FFT filter to remove photgraphic paper texture

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  #51  
Old 11-16-2005, 11:21 AM
Bmud Bmud is offline
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Here's what I've found about the FFT:

Each quadrant is a stretched copy with a 90*x degree rotation about the center of the image. If you don't believe me, run the FFT on a square image with even-numbered dimensions and then duplicate one quadrant into the remaining three with the difference blending mode. You'll get perfect black.

Here's what I've done to improve the process:
1. Copy the noisy document to a new document & flatten.
2. Increase canvas size by 400px on X & Y with 50% gray background color.
3. Run the FFT RGB filter.
4. Copy the Red channel to a new layer.
5. Make a new layer.
6. Knock out the white stars with a black star brush on the top part of the image.
7. Duplicate the layer with the black stars.
8. Make a new temp layer and just dump whatever color into it.
9. Link the duplicate and the dump layers.
10. Rotate the dump layer 180 deg.
11. unlink & delete the dump layer.
12. link the two star layers & the copied red channel & CTRL-E to merge linked.
13. Copy all. Hide the layer. paste into the red channel with the background selected. Delete that extra layer or just flatten.
14. Run the IFFT filter.
15. Copy & paste some of the "striping" that's in the grey area, (usually it's vertical) stretch it over the whole canvas, and invert & set to hard light 50%. I'm not sure why it shows up in the first place.
16. Crop off the extra 400px & slap the grey image onto the original. Run median on the color part. Woo. Done.

Now then, what I havn't been able to figure out when enough is enough. At what point do i say "This star is too small. if I knock it out with black then I'll just get a big cloudy mess." I have a feeling that I should be using grey to knock out stars sometimes instead of black -- like when they get really close to the center. Sometimes it seems like being quick and dirty about knocking out stars is better than being maticulous.

[For example], This picture turned out fine, but sometimes I get cloudy mess all over the place.

[MINI FFT TUTORIAL]
Attached Images
File Type: jpg mini.jpg (97.9 KB, 64 views)

Last edited by Bmud; 12-22-2005 at 01:35 PM.
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  #52  
Old 11-16-2005, 02:44 PM
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byRo byRo is offline
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Hi there, Bmud. Welcome to RetouchPRO
Thank you for a very interesting post.

- As I see it each quadrant would be a mirrored copy, and not a rotated copy. Other than that, yes agreed .

- Are you sure you posted the right brush? I had imagined something star-shaped (which would be a great idea) but what came out was an "alphabet" brush.

- In your "example" picture, I think you've painted out way too many stars. If you are trying to eliminate paper texture, then only the larger stars of the central diamond need painting. If you follow the repetitive pattern of these stars you'll find a few other less obvious stars that may still produce unwanted texture (see attachment). The other small stars may be due to some element of the actual image, or the effect of the 400 pixel border that you added - and should be left alone;

- The striping trick is quite neat, I'll have to try that out. As to why it happens - my theory would be that when we replaced the stars with black holes we threw away some information that would be needed at the edges;

- I too have the feeling that some sort of an average grey would be better than just pure black. When I defended this I got shot down by the theorists, but I haven't given up yet.

- As to when is enough. The important stars, due to the paper texture form a regular pattern around the centre. These are the only one's you need to paint - but be sure to get them all. If you are getting close to centre, then you're probably knocking out something important from the image and not unwanted paper texture.

Hope to hear more from you,

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File Type: jpg fft_omg-byRo.jpg (98.8 KB, 85 views)
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  #53  
Old 11-23-2005, 11:35 AM
Bmud Bmud is offline
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I fixed the FFT Brush download. Thanks for the tip. I'm probably going to save a bunch of time now.

The behavior seems to vary, but no doubt the images are completely identical when the top is rotated 180 degrees and brought to the bottom.
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File Type: jpg fft_omg2.jpg (99.3 KB, 49 views)

Last edited by Bmud; 11-23-2005 at 11:47 AM.
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  #54  
Old 11-23-2005, 12:17 PM
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byRo byRo is offline
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Fun (1) things to do with the FFT.....

- Do a big radial blur from the centre - makes an "arty" halo effect;

- Double the size (centre and crop) of the Red channel. As I remember (can't check now) you get 4, quarter-sized, almost identical versions.


(1) Some people, like me, have a wierd definition of "fun"
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  #55  
Old 11-23-2005, 02:54 PM
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Caitlin Caitlin is offline
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Quote:
Originally Posted by byRo
- In your "example" picture, I think you've painted out way too many stars. If you are trying to eliminate paper texture, then only the larger stars of the central diamond need painting. If you follow the repetitive pattern of these stars you'll find a few other less obvious stars that may still produce unwanted texture (see attachment). The other small stars may be due to some element of the actual image, or the effect of the 400 pixel border that you added - and should be left alone;
Oh! I was unaware of this, I've been painting out everything but the central large star. It's not what you have in the tut though?
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  #56  
Old 11-23-2005, 06:20 PM
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byRo byRo is offline
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Quote:
Originally Posted by Caitlin
..... It's not what you have in the tut though?
Oops, you're quite right. I'll have to fix that.

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  #57  
Old 11-25-2005, 10:02 AM
Bmud Bmud is offline
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Basically, if you increase your canvas by 400px, then any star that's 400px away from the edge (or less) can be ignored. That alone has saved me a bunch of time.

I like the Radial Zoom effect! That'll come in handy the next time I need to make something dirty-looking

Check this out, a moire nightmare... I've tried FFT on this, but the dot pattern is really big compared to the whole image (I think)
www.osysi.net/files/fft/fft_nightmare.png

Last edited by Bmud; 11-25-2005 at 10:39 AM.
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  #58  
Old 11-25-2005, 01:55 PM
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Panpan Panpan is offline
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There were certainly a lot of stars in the fft!

For color, I blurred the a and b channels in LAB mode. After the fft, I ran eat Image, corrected and sharpened, then ran Neat Image again. I thought I would get rid of the remaining pattern by running the fft again, but there were no stars left to blacken .

Pierre
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File Type: jpg fft_nightmare.jpg (88.7 KB, 71 views)
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  #59  
Old 11-26-2005, 03:47 AM
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byRo byRo is offline
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Bmud, you're sure bringing up some interesting points here.....

1) Moire - For me, at least, moire patterns are caused by the interference of two high frequencies resulting in a new perceived low frequency. The "dot Pattern" on the picture you posted probably has another name (which I don't remember now).

2) Texture x Colour - For the images we've been considering in the tutorial the superimposed pattern was due to physical texture ridges of the paper on which the photograph was printed. In your image the pattern is not superimposed, rather each colour has a patterned disposition.
What this means is that when we do the FFT process it is not enough just to consider the luminosity, you should process each channel separately (see attachment)

3) I downloaded your FFT brush again, and got an alphabet again - maybe I'm doing something wrong. Anyway, based on (what I believe was) your idea, I made my own (see zip attachment). Actually it makes star painting easier because you can line just up the horizontal and vertical line and hit the star right on.

Attached Images
File Type: jpg fft_night_G.jpg (96.5 KB, 61 views)
File Type: jpg FFT-Nightm-Compare.jpg (92.6 KB, 83 views)
Attached Files
File Type: zip fft_brush-byRo.zip (5.8 KB, 66 views)
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  #60  
Old 11-27-2005, 04:10 AM
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bart_hickman bart_hickman is offline
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I took what Pierre did and ran the jpeg artifact remover in PSPX. That's the (1st attachment). Followed that with the PSP NR tool (2nd attachment)

Bart
Attached Images
File Type: jpg fft_nightmare_nojpeg.jpg (83.1 KB, 70 views)
File Type: jpg fft_nightmare_nojpeg_NR.jpg (78.1 KB, 73 views)
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