[Tex2002ans]

Does anyone have a method for detecting/removing lines in scans WITHIN text?

I think this would really help towards cleaning up PDF scans from Archive.org and elsewhere.

The Problem

(These sample images were cleaned up manually: Before = ScanTailor, After = Manual Cleanup.)

"Easy" Lines

These type of lines occur where the line barely intersects with text:



"Hard" Lines

The worst though, are lines which go through the middle of text.

What I would ultimately aim for is Before/After:



Potential Solutions

This is some of the research I've done so far:

#1: Hough Lines (ImageMagick)

To detect lines within images, I ran across "Hough-Line Detector" in the ImageMagick Manual.

This site+script shows how Hough Lines can detect lines within images (photographs):

http://www.fmwconcepts.com/imagemagick/houghlines/
https://www.imagemagick.org/discours...ic.php?t=25476

Towards the bottom of the fmwconcepts link, it shows how to detect the horizon (or a fence) by inverting the image.

Maybe there's a way to use inversion to detect vertical lines easier:



Related: And here's a different forum post using Hough Lines to detect page boundaries:

http://www.imagemagick.org/discourse...ic.php?t=31321

(Although I find ScanTailor already does a decent enough job at page boundary removal.)

#2: ImageMagick (Removing Lines Outside of Text)

Some of these examples show removing horizontal/vertical lines... but these are straight lines with no breaking in between:

Remove Vertical Lines for Pre OCR (Tesseract)

These show removing table borders from an image:

https://stackoverflow.com/questions/...s-programmatic

https://stackoverflow.com/questions/...ize-from-image

#3: Baseline Detection + Vertical Line Detection

Perhaps there is a way to combine "baseline detection", with a "vertical line detector"... to at least delete MOST of the vertical line automatically.

Even this would be a huge help over complete manual cleanup.

(I roughly put these images together in GIMP. Still haven't figured out how to get ImageMagick to do this.)

Step 1. Detect Baselines + Expand:



Step 2. Detect Vertical Line (potentially use Hough Lines?):



Step 3. Automatically remove vertical line that DOESN'T overlap the baselines:



While not as good as manual cleanup, this would make the text much more readable + OCR-friendly. See Original + "Automatic" + Manual pages side-by-side:



Related: Here's ImageMagick being used to add Line Numbers to an image. Perhaps something from here can help detect baselines.

* * * *

Hoping everyone can put their minds together and come up with some solution.