[Panpan]

Originally Posted by Cameraken

2) Flatten all Layers
You may not need this but, for precaution, flatten all the layers...<alt><L>, <F>. This is because FFT doesn’t understand layers, masks, alpha channels etc. The image must be just one “Background” layer and nothing else;

This is not correct. Just put a black layer behind the fft layer.

Pierre

[ebbtide]

Ro, I followed your additional instruction and got two gray scale images but all was OK once I realized that the color didn't return until the luminosity blending was selected, then everything was ok.

Because the FFT is a symmetric math function made of cosines you only need to paint out the stars on either the left side to the vertical axis or from the right side of the image. Saving a little painting time if you have a lot of unwanted frequencies in your image. Thanks for the instant help Ro !

[byRo]

Originally Posted by ebbtide

Because the FFT is a symmetric math function made of cosines you only need to paint out the stars on either the left side to the vertical axis or from the right side of the image.....

Are you sure about that?
I can understand the logic, but it seems strange that 50% (or maybe 75%) of the information is just waste.
Also, if I paint just one side how is the IFFT function going to know which side it should consider, original or painted?

It would be nice if it was true, but I think it's unlikely.

Rô

[Cameraken]

Pierre

I went to http://www.pages.drexel.edu/~avc25/archive.htm#FFT to try to find some more information. But is sadly lacking and does not say if a picture can be on layers.

However I did do some tests.
When you run FFT on a layer then the texture from only that layer is removed and the image comes back transparent (hence the black layer required) but this gives darker results than working from a flattened picture.

I can’t understand why you would want to work on a layer as texture removal should be the first step in the workflow

My Quote was not my words but an extract of step 2 in the tutorial and I think it is a sensible precaution and should be left as it is.

Ebbtide
I also tried your method and still had texture in the picture

Ken

[ebbtide]

Yea, I shot too fast on saying you could only do half the symmetric star pattern. I scanned a newspaper picture and did my grand experiment. Painting out half worked as well as painting all. But on retrospect I guess it was because it was such a bad image I couldn't see the difference. On trying a high quality image with interference in it, you do definitely need to paint out all stars. Sorry for the fire drill guys.

[Bmud]

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]

[byRo]

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,

Rô

[Bmud]

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.

[byRo]

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.

Rô
(1) Some people, like me, have a wierd definition of "fun"

[Caitlin]

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;
Rô

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?

[byRo]

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.

Rô

[Bmud]

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

[Panpan]

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

[byRo]

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.

Rô

[bart_hickman]

I took what Pierre did and ran the jpeg artifact remover in PSPX. That's the (1st attachment). Followed that with the Paint Shop Pro NR tool (2nd attachment)

Bart