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FFT and Golf Balls

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  #21  
Old 05-26-2005, 04:19 PM
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jcr6 jcr6 is offline
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answers to Cameraken

Quote:
I have a few Questions
I am (now) Using FFT_RGB_PlugIns_13April_2005. Is this the version everyone else is using? And is this the correct version?

In http://reindeergraphics.com/tutorial...fig_4_13_6.jpg
The corners are missing. Is this significant?

Step 6) Any suggestions?

You suggest starting with a B&W image. Do you mean Greyscale or RGB>Desaturated. My Fourier Transform Folder is unavailable with a Greyscale Image

In the UK Ilford used to make a paper called Velvet Stipple. This was one of the most textured papers available. Does anyone have a sample for Jcr6 to deconstruct.
As you may have guessed, I'm not using FFT RGB... Where do I get it?

The corners are "missing" but aren't really missing. It turns out that they're considerably lighter because they've been reduced so much in power. This is a side-effect of the Butterworth filter. The banding in the image is a result of compression.

The reason I suggested B&W was because there is a different signature in the different color channels -- this is more evident if you're looking at a scanned image from a magazine where different colors have different screen angles.

You might also try scanning a blank piece of Velvet Stipple and performing an FFT on that -- this should give you your definitive map of bad frequencies.

Fovea works on one channel at a time.
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  #22  
Old 05-26-2005, 05:25 PM
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Quote:
Originally Posted by jcr6
As you may have guessed, I'm not using FFT RGB... Where do I get it?
This is the Alex Chirakov filter, you'll find it here.
It's called RGB because the earlier verison encoded the FFT information into HSB, now it´s a lot easier because the FFT is in the Red and Green channels.

OBS: (for jcr6) it will take any size of input image

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  #23  
Old 05-26-2005, 07:49 PM
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Cameraken Cameraken is offline
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For byRo

byRo

Thanks for answering jcr6. I was just about to reply
When I follow your link there are 2 Options
Option 1)
Download new version of FFT/IFFT Photoshop plugin - 235Kb (April 2005)
Option 2)
Download RGB version of FFT/IFFT Photoshop plugin - 156Kb (April 2005) (Red and Green channels are used instead of Hue and Light to store complex phase and amplitude information)

I have downloaded the second option which seems to follow what you have been saying. I this correct?

It is important here that we are all talking about the same filter.

I had added steps 1 and 2 (and what is now 4) because of what I read from jcr6. But from what you are saying they are not needed with Alex Chirakov filter (and I did not notice any improvement from this)
So. New Steps

1) Image > Adjust > Desaturate
2) Filter > FFT RGB
3) On the Red Channel > clone (using Darken) out the Stars except middle one
4) Blur step here? (Butterworth?)
5) Filter > IFFT RGB



Proxy has submitted what looks like Velvet Stipple Here
http://www.retouchpro.com/forums/image-help/10633-photo-paper-texture-problem.html

I was a Professional Photographer for over 20 years and have copied hundreds of photos. Before digital this was easy I put a print on my copy stand got my trusty H/Blad and made copies without worrying about texture as my lighting eliminated it. The problem is caused by scanners which have directional lighting. Why can’t they invent a scanner with a light around the sensor?

Ken
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  #24  
Old 05-26-2005, 10:04 PM
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Caitlin Caitlin is offline
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Sorry for being a bit dense here - but can I just confirm something that is probably bleeding obvious:

6th step - overlay with original image set to color mode? Or is there some other way of getting the colour back?
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  #25  
Old 05-27-2005, 01:10 AM
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Gary Richardson Gary Richardson is offline
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Ro, tried downloading the RGB version, but can't open it. (its a rar file, can't find any info on it).
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  #26  
Old 05-27-2005, 06:45 AM
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Caitlin
Put the repaired B&W layer above your colour layer and set blending mode to Luminocity (thanks Flora)

Gary
A rar file is a compressed file you will need a program called Winrar to open it
There is a demo available here
http://www.rarlab.com/download.htm
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  #27  
Old 05-27-2005, 06:48 AM
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Gary, didn't quite understand if you don't know about RAR files or if this one was corrupted.

Anyway - general instructions for all...

- You will need WinRar to open the ".rar" files, homepage here. It's shareware, but doesn't stop working after the time limit (just nags).

- If it's the second, better download again.

- When you've got it open in WinRar, open the "bin" folder and extract the two ".8bf" filters to your PS filters folder.

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  #28  
Old 05-27-2005, 06:59 AM
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Thumbs up You're only correcting the luminance channel!!!

I just realized that you're only correcting the brightness information, not the color channels.

(One of those "Aha!" moments!)

In order to do this correctly, you really have to correct ALL THREE CHANNELS. And, there can be a different pattern in each. In the case of the "Golf Balls" they're refracting light, so the PowerSpectrum for each (R, G, B) will be different.

If you don't do this to all of the channels, your colors will be screwy -- and will retain the golf ball pattern.
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  #29  
Old 05-27-2005, 07:22 AM
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Morning, Camaraken - beat me by three minutes!

Quote:
Originally Posted by Cameraken
6th step - overlay with original image set to color mode? .......Put the repaired B&W layer above your colour layer and set blending mode to Luminosity
They are in fact exactly the same thing, the Lumosity is more efficient because you don't need another layer.

Quote:
Originally Posted by Cameraken
1) Image > Adjust > Desaturate
I wouldn't do this. When you do the FFT you will be working on a greyscale image (in RGB mode). After the FFT process, as you rightly said, you mix in Luminosity. It would be much better then if you separated the Luminosity and not Desaturated (they are very different). Then you process FFT and mix back in the clean Luminosity.

To get Luminosity: New Layer (<Ctrl><J>), Edit>Fill - 50% grey, color, 100%. (There are other ways, this is the quickest)

Quote:
Originally Posted by Cameraken
4) Blur step here? (Butterworth?)
Don't think this would help any.

So summing up...
1) Duplicate original image, right click on title bar (that's a new image, not just a layer);
2) On the new image, get Luminosity (as above);
3) Flatten all, <Alt><L><F> (FFT does not understand layers);
4) Run FFT RGB;
5) Clone out stars in the Red Channel;
6) Select all channels again (easy to forget this bit), and run IFFT RGB;
7) Slide this layer on top of the original image (with <Shift> pressed, to align);
8) Set this new layer's mode to Luminosity.

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  #30  
Old 05-27-2005, 08:07 AM
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Quote:
Originally Posted by jcr6
In order to do this correctly, you really have to correct ALL THREE CHANNELS. And, there can be a different pattern in each....... If you don't do this to all of the channels, your colors will be screwy -- and will retain the golf ball pattern.
The theory is solid, OK. But in practice you'll be doing more than three times as much work (including channel separation and recombination) and the difference in the final result jsut isn't worth the trouble.

I did it and, in fact, I found that the Luminosity way gave a slightly better looking result (but then again, I may be biased because I expected it to)

[Geekstuff]My litte theory - The eye responds much better to luminosity than to colours (JPEG compression reserves 4 times more space for Luminosity information). If you do FFT separately in each channel then you run the risk of introducing Luiminosity artifacts that weren't in the original[/Geekstuff]

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