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FFT and Golf Balls

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  #81  
Old 06-09-2005, 04:34 PM
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byRo byRo is offline
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Quote:
Originally Posted by Greek FFT
Fourier will be gnw'rjmi significance.
..took the words right out of my mouth!!

Quote:
Originally Posted by Cameraken
1) Again another confirmation that the stars should be painted out in black
Yes, but he's painting black in all the channels, not just the Red one;

Quote:
Originally Posted by Cameraken
2) They are using a square picture as an example but do not seem to insist on square
They're using the Chirakov filter so it can be any size and shape;

Quote:
Originally Posted by Cameraken
4) They are using gaussian blur on the final image to clean up further.
I think maybe he's blurring the original "coloured" layer and not the FFT luminosity layer - which is a good tip that we hadn't mentioned before.

Caitlin, I got the hint - now I going to write it in portuguese, OK?


Yeah Duv, I know........
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  #82  
Old 06-10-2005, 04:45 AM
jocker jocker is offline
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Quote:
Originally Posted by Caitlin
For whoever is planning to do the FFT tutorial, I happened upon this one - Rather nicely done - a shame it's in Greek!

FFT tutorial (Or in this case babelfish English) The original is here: http://www.dpgr.gr/index.php?page=FourierPS
Well, being greek and thus able to read the original of that post, I can tell you 1 thing for certain.. The person writing the article is clear in that he does NOT want to create a tutorial, but rather he just wants to proove a point, that being that everything is just plain-old maths. The steps mentioned are as Cameraken said, but he also mentiones that one should always try to use a "circular pattern" symetric to the center star when deleting spikes.

"Again another confirmation that the stars should be painted out in black"
Well, actually he says that one should "mask-out, filter-out, delete or whatever" the white stars, claiming it's just a matter of terminology and does not actually make much of a difference... not very precise I'd say

If anyone is interested, I could write an exact translation of that article, but I seriously doubt that it would shed any light to the subject. the posts here are much more precise and helpfull than anything I have found on there (and FFT is the one reason I keep coming back to retouchpro over and over again)

Thnx...
Jocker
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  #83  
Old 06-10-2005, 05:56 AM
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Flora Flora is offline
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Hi Jocker,

Welcome to RP!

We do hope you'll keep coming back ... and, boy, are we glad you shed some light on this ....

As you can see Rô had nearly finished translating the tutorial...even though, I think he was struggling a bit to stay as close as possible to the original text here...
Quote:
Originally Posted by Greek FFT
Fourier will be gnw'rjmi significance.
Quote:
..took the words right out of my mouth!!


Thank you very much for your help!
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  #84  
Old 06-10-2005, 06:23 AM
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jocker, welcome to RetouchPRO!!

Thank you very much for the help.
Promise I'll post the tutorial this weekend, promise

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  #85  
Old 06-10-2005, 09:00 AM
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Cameraken Cameraken is offline
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Welcome Jocker and thanks for your input.
‘Everything is just plain-old maths’
When you scan a picture it just becomes a set of numbers, which can be changed or manipulated. The Alex Chirakov FFT RGB is just a calculation on these numbers.
The whole thing could be done in Excel or Visual Basic in fact I have a visual basic program for removing noise from sound, which uses the same calculation.

The point about symmetry is a good one and makes sense with the maths.

I don’t think it is necessary to translate the whole thing but can you help with the gaussian blur bit. It sounds a bit like Floras 'cleaned the composite' step. But as byRo says it sounds like they are talking about the colour layer.

Ken
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  #86  
Old 06-11-2005, 07:15 AM
jocker jocker is offline
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Quote:
Originally Posted by Cameraken
Welcome Jocker and thanks for your input.

I don’t think it is necessary to translate the whole thing but can you help with the gaussian blur bit. It sounds a bit like Floras 'cleaned the composite' step. But as byRo says it sounds like they are talking about the colour layer.

Ken
ok, let's try a word-by-word translation of the whole thing, so that noone thinks that he's actually missing some intresting point from that article because it's in greek...

----------------------------
Translating http://www.dpgr.gr/index.php?page=FourierPS
----------------------------

Let's see how a fourier transformation of our ewample looks.
Since the information is pictured through the frequency spectrum, and the noise is periodical, like magic, all the noise is shown on specific places, much easier to process. (we use the filter Fourier Transform->FFT):
[picture of fourier spectrum here]
Doesnt it look odd that from this picture we can go back to the original? Notice how symmetric to the main star the bright points are. These are our noise. So what do we do? We delete, mask-out, filter-out, it's just a matter of terminology
Using paintbrush we blank-out the aforementioned points, as in the picture bellow. The process was delibaretly done roughly so as to show that even this way, the method gives very good results.

[picture of EDITED fourier spectrum here]

Time to go back to the space domain from the frequency domain... (that's what a mathematician would say), we just apply the inverse filter and go back to the original picture: (Fourier Transform->IFFT)

[grayscale transformed picture here]

Look at how clean the picture looks. The fact that it's grayscale (that's how the filter FFT works, at first it transform it into grayscale and then applies the transformation), wont make it more difficult to us, it's enough that the luminocity is cleared.

We take a copy of the original picture, put it over the final one as a new layer with blending mode set to colour and we apply as much gaussion blur needed to get rid of the noise (No detail is lost, as that is in the underlying layer).
Here is the result:

[final picture here]

and a crop of before and after, blown up by 200%:

[blown up crops here]

Frequency domain transformation requires skills and experience. Good thing that there are various filters and utils that hide these dificulties

The reason for this article was not to suggest that one should do this by hand, but to shed some light into how applying such methods can give very good results.

--------------- End translation -----------------

See ya...
Jocker

Last edited by jocker; 06-12-2005 at 05:36 AM.
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  #87  
Old 06-11-2005, 01:23 PM
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Cameraken Cameraken is offline
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Thanks Jocker for taking the time to do that.

Byro was right (as usual) :- ‘gaussion blur the colour Layer as much as needed to get rid of the noise No detail is lost, as that is in the underlying layer.’

That’s worth noting in case the info has come too late for byRo tutorial.

Thanks again Jocker.

Ken
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  #88  
Old 06-12-2005, 02:21 AM
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Flora Flora is offline
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jocker,

This is just great!!! Thank you again for your time and help!!!!!

Ken,

... about blurring the 'color' Layer ....
it is right you don't lose details ... but, if to fade the noise you use the Gaussian Blur, careful because the colours tend to 'bleed' into each other so you can get 'noise-free' pink teeth or, if you are working on a portrait, the skin around the edges tends to get the background tinge ...etc. So, in this case, I would rather use the Median Filter as noise remover, as the Median Filter tends to 'recognize and respect' the edges between colours ....
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  #89  
Old 06-12-2005, 05:43 AM
jocker jocker is offline
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Quote:
Originally Posted by Flora
This is just great!!! Thank you again for your time and help!!!!!
You're welcome.. I've been quietly reading the forum since January, originally trying to find a decent way to remove the honeycomb effect as a favor to my girlfriend. I'm not really into photography, thus have not contributed anything all this time... Glad to be of service since you have all helped us quite a bit.

Jocker
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  #90  
Old 06-12-2005, 02:03 PM
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byRo byRo is offline
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Quote:
Originally Posted by Flora
[...So, in this case, I would rather use the Median Filter as noise remover, as the Median Filter tends to 'recognize and respect' the edges between colours ....
Nice one, Flora
I'd forgotten that.

I've written the FFT tutorial but the "uploader" isn't cooperating with me this weekend, so I haven't been able to post it yet.

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