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Fourier Transform Plug-in - get rid of "newsprint dots"

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curvemeister:
Today I discovered a free plugin that does Fourier Transforms, offered free of charge at a site specializing in forensic software.  This is a Windows plugin, and will work in both Photoshop and Photoshop Elements, as well as any other program supporting Photoshop plugins.

There are a number of interesting things you can do with this plugin, but one of the coolest is the removal of halftone dots and paper patterns from your images.  If you have not used Fourier transforms this way before, believe me this is light years away from simply blurring the image to get rid of the dots.

The plugin and documentation, including an example of removing halftone dots from a thumbprint image are here:

http://home.planet.nl/~ber03728/4N6site/improc/fftplugin/howto.htm

I will be providing my own example shortly, but I suggest that you download their thumbprint image, and walk through their example carefully.  You will be rewarded with a technique that will  be worth its weight in gold, next time you encounter a valuable image that is available only via a newspaper or magazine print, or a family portrait that is printed on textured paper.

A couple of hints about the demo.  When the diagonal banding is removed, note that this is done by removing the relatively subtle diagonal lines near the very center of the FFT pattern.  Removal of the halftone dots may be done by simply blacking out the center of each star-shaped pattern, rather than by usinig the clone tool as discussed in the howto.

Mike

Frits:
Mike,

it looks nice to me!
But first , I must discover how to get Channels in P.S.E. 4.0.
The effect-plugins of hiddenpower  worked all with layers!

frits

unbecannt:
looks interesting
now i may be able to find a practical use for all that fourier theory i had to learn many years ago

curvemeister:
Here is a halftoned image that I've cleaned up using the FFT plugin discussed at the beginning of this thread.  The process is as follows:

1) run the FFT plugin as discussed in the first article of this thread.
2) select the red channel in the channel palette
3) paint out all of the "stars", except the very center one.
4) select RGB in the channels palette, and run the inverse FFT plugin
5) no dots!

This is the only method of removing the dots that actually appears to reveal additional information in the image, instead of merely degrading it.  Although this is a black and white image, the same procedure works with color images with the following modification:  Duplicate the image to a new layer, and when you are done, set the mode of your "descreened" layer to luminosity to restore your color image.

Elements does not directly support editing individual channels.  See the next article in this thread for how to modify only the red channel using Elements.

Mike

curvemeister:
Here's a way to use the FFT plugiin with Elements.  This procedure uses a Levels adjustment layer to hide the green and blue channels, and a cyan multiply brush to erase only the red channel.
 

* dupe the image
* add a levels adjustment layer to the duplicate, and set the output levels to zero for the green and blue channels.  The image will appear red.
* click on the background layer, and run FFT on the new image.  You'll see the characteristic star pattern in the red channel.
* set the foreground color to cyan RGB(0,255,255)
* set the brush mode to multiply
* use the brush to black out the stars other than the center star
* run inverse FFT
* drag the modified image from the layer palette onto your original image
* set the mode of the new layer to Luminance
* run gaussian blur on your original image, with the radius set to about 2.0.

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