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Mailinglist:PanoTools NG
Sender:Joachim Durchholz jo@...
Date/Time:2018-Feb-23 16:43:33
Subject:What would be the best approach for despeckling/denoising?


PanoTools NG: What would be the best approach for despeckling/denoising? Joachim Durchholz jo@... 2018-Feb-23 16:43:33
Hi all,

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 

Use case: I have to scan a lot of pages, and I want to get as much 
quality out of the scan as possible.
It's a six-digit number of pages, so automation trumps everything, 
closely followed by quality :-)

Approach I am currently exploring: Each page is scanned multiple times, 
and the bitmaps are used to identify the random stuff (noise, one-time 
dust specks), leaving me with a bitmap with what's present every time.

- The pages tend to be slightly differently oriented; in extreme cases,
   the angle between scans might be as much as 10°.
- There's some automatic cropping inside the scanner's firmware that I
   cannot fully control. The same page might come out with the whitespace
   around the text cropped, or not.
- The scanner motor might go slightly uneven, so the pages might be
   slightly distorted. I don't expect much variation here, but I noticed
   that some stitching tools work at sub-pixel accuracy (which totally
   makes sense to me), and I would not find it surprising if the scanner
   turns out to have some sub-pixel inaccuracies here.
   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%

TL;DR facts:
- No lens distortion, obviously.
- I can run the scanner at 300 and at 600 dpi.
- Scanner will have to run in color mode. Greyscale processing is an
   options, but I will want to retain the color tint of each page
   (rendering intent is perception).
- I have made an ICC profile of the scanner (with the help of a Wolf
   Faust calibration target).
- The final bitmaps after quality-improvement processing should look
   as if somebody scanned with a higher-quality scanner at 300 dpi.
- The originals will go to the trash after the scans are done, so
   keeping as much quality as possible is an important subgoal.

Posted by: Joachim Durchholz <#removed#>

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