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
case?
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.
Challenges:
- 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%
steady.
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.
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Posted by: Joachim Durchholz <#removed#>
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