How to scan documents

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Revision as of 05:32, 5 December 2010 by Brian Wilson (talk | contribs) (→‎OCR)
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Scan

I have access to a Brother scanner that has a document feed on it. It scans a multipage doc and puts the output into a PDF file on my server via FTP.

  1. Scan the odd pages, front to back, resulting in a single PDF file.
  2. Scan the even pages, back to front, resulting in a second PDF file.
  3. If you have it, you can use Adobe Acrobat to collate the files into a single PDF.

I scan at 300 DPI grey scale, with the scanner doing conversion to PDF and upload to a server via FTP. 300 is probably overkill for text but line art looks good. I note also that for the manuals I just scanned I can actually see ghosts of what's printed on the other side of two sided pages.

OCR

Run gscan2pdf and you can perform all the steps needed to go from raw scan to polished PDF doc.

  1. Start it up.
  2. File->Import to load the raw PDF
  3. Tools->Threshold will help eliminate the ghosts.
  4. Tools->Cleanup to run 'unpaper' over the doc. This will clean up the pages and deskew them. The pages get cockeyed when they go through the ADF (automatic document feeder) and this straightens them up.
  5. Tools->OCR - select an engine, GOCR, Tesseract, Cuneiform are the choices.

In my test, I ran Tesseract over the entire manual and watched the console window. I saw errors on some pages.

Doing the OCR creates a text version of each scanned page, that allows the PDF to be searchable.

Compress

I am trying out the djvu format, it seems like a good way to manage the scanned pages. Compression is very good. See http://djvu.org/

DJVU is an alternative to PDF. It uses wavelet compression.

Ubuntu Notes

Packages under Ubuntu are

  • poppler-utils (PDF utilities)
  • psutils (Postscript utilities)
  • tesseract (OCR software)

Installing the gscan2pdf package pulled in sundry and various useful things such as cuneiform (the OCR program that Canonical has blessed at 10.10) and djvu2pdf.

On the Mac I use the viewer djview-libre which is also available for Linux and Windows.

See also

How to scan and OCR like a pro with open source tools from the Linux.com site

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