On 11-05-26 6:08 PM, John Sessoms wrote:
From: John Sessoms
Ok, so I had a go at seeing what I could do at restoring the image using
the tools Bruce linked to.
Never mind. I took another look at the corrected image Bruce had
posted and took my attempt down right away.
Got to install imagemagick & see if I can figure out how to use it.
The Photoshop plug-in doesn't seem to work as well as imagemagick.
John, I believe they both use the same FFT engine, the opensource
project FFTW.org, so I'd expect that they should work about the same,
given the same inputs.
What did your spectral mask look like? You may not have removed enough
points. I iterated on that image a couple of times, removing more
spectrum each time before I was satisfied that I'd suppressed enough of
the original's vertical lines.
Here's the image I got for the frequency space in Dave's (leveled and
cropped) original:
http://dl.dropbox.com/u/2254722/picture0001_spectrum.png
And here's the mask I ended up with, created in Photoshop by painting
black onto a white layer with a 10% hard brush:
http://dl.dropbox.com/u/2254722/picture0001_spectrum_mask2.png
You don't want to allow any hard edges in the mask as that will create
new artifacts (especially ringing near any edges), so you must either
use a soft-edged brush or apply Gaussian blur to your mask before
applying it.
When creating the mask I looked for anything in the frequency-space
image that seemed regular and symmetrical. Normally an image like that
(especially such a soft one) should have a pretty uniform and random
looking spectral distribution, so any dense white clusters or stars are
suspect. As you can see I was fairly sloppy with my hand drawing of the
mask, but it doesn't seem to matter all that much, so you can fairly
safely err on the generous side.
A quirk of the FFTFILTER script is it expects the input image and the
mask image to be the same dimensions, so I expanded the canvas of the
original image (to 2092x2092) making it square, with black bars above
and below.
http://dl.dropbox.com/u/2254722/picture0001-2092.png
When you install ImageMagick on your computer, make sure that the FFTW
library is already installed for it to find, or it won't be able to do
any FFT operations. If you get error messages when trying to run the
script, Googling on those messages will get you lots of help on the
proper configuration of this stuff.
Good luck!
-bmw
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