That is a pretty impressive piece of work, Bruce. Given that you were
working with a scan of a copy, it's an excellent approach to the problem.
Here's a bit of general advice:
For an original print with texture issues, it is often better to shoot the
original with a camera rather than scanning. Some scanner light sources,
like the Epson V700 I use, tend to bring out more texture than is desirable.
In my experience use of a conventional two-light copy setup often hides
texture and surface defects much better than the scanner. It's also
possible to reduce texture further by playing with reflectors and/or
additional light sources.
In general, I prefer scanning prints because sharpness is better than, say,
a 15 megapixel digital. There are times when using a camera makes more
sense, though.
cheers
John Poirier
----- Original Message -----
From: "Bruce Walker" <[email protected]>
To: "Pentax-Discuss Mail List" <[email protected]>
Sent: Thursday, May 26, 2011 4:50 PM
Subject: Re: OT Picture fix help
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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