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Mailinglist:PanoTools NG
Sender:Erik Krause erik.krause@...
Date/Time:2018-Feb-26 14:59:40
Subject:Re: What would be the best approach for despeckling/denoising?

Thread:


PanoTools NG: Re: What would be the best approach for despeckling/denoising? Erik Krause erik.krause@... 2018-Feb-26 14:59:40
Am 23.02.2018 um 16:43 schrieb Joachim Durchholz:

> this is somewhat tangential to panorama stitching, but some of the
> things that a panorama stitcher does apply to my use case as well, so I
> hope the panotools are useful anyway.
> 
> Since the use case description is MUCH longer than the question, let me
> write the question first:
> What tools should I look at first to get a working toolchaing for my use
> case?

Sorry for being late...

I'd use vuescan for scanning. It has built in multi pass scanning. 
Actually two types, but their availability depends on the scanner: it 
either scans one page multiple times or it reads the scan line multiple 
times before it's advanced. The second case would mean there is no 
alignment problem at all. In fact vuescan does the averaging itself.

However, multi pass scanning is intended for high dynamic range scans 
like slides or negative film. It shouldn't be of any benefit when 
scanning paper, where the dynamic range is fairly low by nature.

I'd focus on image manipulation techniques to reduce noise, dust and 
speckles. The usual way is to use a sequence of minimum and maximum 
filters to smoothen the characters and remove bad pixels. The minimum 
filter colors the pixel in question with the minimum of the surrounding 
pixels, effectively shaving one or more pixels from all dark areas. 
Anything that is smaller than the chosen radius will be eliminated. The 
maximum filter does the opposite, it makes dark areas larger by it's 
radius, such restoring the original character's weight, but with 
smoother edges.

Obviously you need to adjust those filters such that characters don't 
get split. Some experimentation would be needed. You should investigate 
ImageMagick, wich is a very powerful command line image editor.

[...]

>     I hope that panotools will be able to detect and correct that effect
>     because similar effects can happen with CCD cameras that are not 100%
>     steady.

Original panotools has correction parameters for image shear like 
typically caused by line scanners as well as for lens distortion and 
image alignment. So in theory you could use a decent control point 
generator to generate control points between scans of the same page, 
then feed those points in a script to PTOptimizer which calculates the 
necessary distortions, then feed the resulting script to PTStitcher, 
which would do the actual warping of the images. Then you could pass 
them to a tool that averages them, f.e. PTAverage.

However, all those tools are very old now and probably very slow 
compared to the more modern tools contained in hugin or PTGui.
(You already asked on hugin list, did you?)

If you want to go that way you can start at
https://wiki.panotools.org/Panorama_scripting_in_a_nutshell

I personally would use PTGui, since I own it and I'm used to it. But on 
the other hand I'd not do multi scanning for book pages anyway.

If you want you can PM me some sample scans (or rather a download link) 
and I'll see what I can do...

-- 
Erik Krause


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