OCR old software listing.

[wrcooke at wrcooke.net]

> On December 26, 2018 at 4:29 PM Mattis Lind via cctech <cctech at classiccmp.org> wrote:
> 
> 
> Finally I got hold of the sources for the PDP-11 SPACE WAR that was
> submitted to DECUS by Bill Seiler.
> 
> The format is scans of the PAL-11S listing output. It is easy to crop the
> image to only contain actual source. Then running OCR on it. Tried a few
> online versions and tesseract.
> 
> The problem is that the paper that the listing is printed on has lines.
> Very black lines. It makes the OCR go completely crazy. Source lines
> without black lines OCR ok. The others do not. The files need massive
> amount of manual intervention.
> 
> Does anyone have an idea how to process files like this?
> 
> A good way to remove the black lines?
> 
> There are only 19 source files with three or four pages each so I don't
> think it makes sense to try to train tesseract to do it (training tesseract
> seems to be a huge undertaking).
> 
> https://i.imgur.com/dvY973s.png
> 
> /Mattis
One thing you might try is to pull the scan images into matlab/gnu octave and do a 2d FFT, remove the frequency band of the lines, inverse fft, and save.  I've had good luck removing regular patterns of noise from images that way.

Will

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