Using the FFT filter to remove photgraphic paper texture

byRo · #1 06-23-2005, 09:49 AM

One problem that can come up from time to time is the need to retouch a photograph that has a heavy paper texture. On such a photograph the use of the day-to-day retouching techniques can be very difficult, as the texture gets just too mixed up in with the underlying image.
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This is not meant to be THE definitive tutorial on FFT. I intend to be altering this tutorial as time goes by and new ideas arise.
Comments are most welcome, and when pertinent will be incorporated into the tutorial.

Rô

Gary Richardson · #2 06-23-2005, 11:50 AM

Thanks for a well written and informative tutorial. I'm sure I'm not the only one who's not totally at home with the FFT filter, and this gives a good grounding in how to use it.

Sorry, I forgot. Yes, the pictures are showing fine.

Flora · #3 06-23-2005, 12:25 PM

Thanks for a great Tutorial, Rô!!!

...and YES ... all your pictures are perfectly visible in Italy as well!!!

jcr6 · #4 06-23-2005, 01:22 PM

1) If you increase the canvas size, filling with gray, by at least 100 pixels on both dimensions before doing the FFT (and doing a new crop afterwards) you can solve the "ringing at the edges" of your image. The provides some padding and cuts in half the amplitude of the step from the top to the bottom. It would be even better to fill that in with the Average of the image, but 128 gray is sufficient.

2) I must really strongly urge using a black brush with solid black in the middle of it instead of gray and especially instead of cloning. Otherwise a small amount of the pattern will remain.

3) The radius 2-3 Gaussian Blur makes me nervous. You're potentially killing a lot of real stuff.

Now, that being said, it is a GREAT TUTORIAL. Very clear and concise and usable without scaring people.

Flora · #5 06-23-2005, 01:32 PM

Hi jcr6,

Quote:

Originally Posted by jcr6

1) If you increase the canvas size, filling with gray, by at least 100 pixels on both dimensions before doing the FFT (and doing a new crop afterwards) you can solve the "ringing at the edges" of your image. The provides some padding and cuts in half the amplitude of the step from the top to the bottom. It would be even better to fill that in with the Average of the image, but 128 gray is sufficient.

You are my HERO!!!!

The "ringing at the edges" was something I had given up on .... I think I tried every single variation, but If I wanted the blasted texture minimized I always ended up with "ringing at the edges"

Quote:

Originally Posted by jcr6

2) I must really strongly urge using a black brush with solid black in the middle of it instead of gray and especially instead of cloning. Otherwise a small amount of the pattern will remain.

3) The radius 2-3 Gaussian Blur makes me nervous. You're potentially killing a lot of real stuff.

Same as before .... (I'm very lazy...)

Gary Richardson · #6 06-23-2005, 02:05 PM

Great tips JCR6, as Flora says, ringing was a problem I did'nt have an answer to.

Thanks.

Caitlin · #7 06-23-2005, 04:10 PM

Thanks Ro! Great job - thanks for responding to the constant nagging! *lol*

Do you think it would be worth amending the introduction to say it can also be used for newspaper print, and any other righly regular pattern? I know my confusion early on with FFT is knowing WHEN I could use it.

byRo · #8 06-23-2005, 04:22 PM

Chris,

Thanks for the great tip. I have included it (with due credit

) in the tutorial.

As to the Gaussian Blur step, I have now changed it to Noise>Median (thank you Flora). It wasn't too clear, and maybe still isn't, but the "blur" is applied only to the colours, not to the luminosity that we just fixed. With the Median filter the possible problem should be even less.

Caitlin,

Well remembered! I'll fit that in somewhere.

Rô

Cameraken · #9 06-23-2005, 06:29 PM

Thanks byRo for a very clear tutorial, the pictures are fine.

Jcr6 has made some excellent points again

One thing that I have learned is that as every picture is different so is every FFT.

There is a posting in the Help requested Forum at the moment called “Can this picture be saves”. If you look at the FFT of this there are no stars only lines. What I did was select the central star with a large feather then invert the selection and Gaussian blur all the line out.
The results are OK. So I suppose once you know how to do things correctly then you can bend the rules as far as you want.

Thanks for the credit byRo (that seems to be your only spelling mistake)

Ken

byRo · #10 06-24-2005, 05:34 AM

Quote:

Originally Posted by Cameraken

....So I suppose once you know how to do things correctly then you can bend the rules as far as you want.

Yep! I've even tried FFT art! Didn't get too far though.

Quote:

Originally Posted by Cameraken

....Thanks for the credit byRo (that seems to be your only spelling mistake)

Ooops. Think I did a portuguese version. Fixed now.

Rô

fat0n3s · #11 06-24-2005, 01:14 PM

Great tutorial ByRo!

Can FFT be used to remove noise as well, or just repeated texture?

jcr6 · #12 06-24-2005, 01:33 PM

We call that "repeated texture" of yours Pattern Noise.

You can implement a blur function, which is good at removing Random Noise with an FFT (including some filters that are much more interesting than a Gaussian Blur). That is pretty much the limit, however. There is no equivalent to a Median filter or the new Smart Blur in Photoshop CS2.

So the answer is "Yes, but..."

...but they're not very useful except in specific cases.

SteveD · #13 06-25-2005, 09:31 PM

Hello -- I am somewhat a pretty novice user of Photoshop CS2 and am interested in the FFT tutorial.

I am having difficulty, however at step 6, the Inverse Fourier Transform. I took particulat note of step 6. When I do the inverse FFT I do not get a grey scale image, I get something like the FFT but colored, no image at all.

I must be missing something. Please help.

SteveD

byRo · #14 06-26-2005, 08:59 AM

Hi Steve, welcome to RetouchPRO

When you said step 6 inverse FFT, I think you meant step 7. Step 6 is just a reminder to turn the channels back on

If you are getting something coloured after the inverse FFT, then I say that you probably did the FFT again and not the IFFT. When things go wrong in the IFFT, you usually get a semi-transparent grey mess.
Try doing the FFT and then the IFFT immediately after, see if that works.

One thing that isn't (wasn't) in the tutorial is that before doing the IFFT the image must again be just one background layer.

Rô

Cameraken · #15 06-26-2005, 02:18 PM

I think I know what Steve is doing

6) Select all channels again
- On the channels palette turn back on the green and blue channel (easy to forget this bit);
- If necessary, flatten the layers (<Alt><L><F>);

It is not enough to simply have the “eye” on the RGB channel as in picture 1
You must have the RGB channel Highlighted as in picture 2

Ken