Originally written by Jens Gulden — see AUTHORS for more information.
pnmunpaper is a post-processing tool for scanned sheets of paper, especially for
book pages that have been scanned from previously created photocopies.
The main purpose is to make scanned book pages better readable on screen
after conversion to PDF. Additionally, unpaper might be useful to enhance
the quality of scanned pages before performing optical character recognition
(OCR).
pnmunpaper tries to clean scanned images by removing dark edges that appeared
through scanning or copying on areas outside the actual page content (e.g.
dark areas between the left-hand-side and the right-hand-side of a double-
sided book-page scan).
The program also tries to detect misaligned centering and rotation of pages and will automatically straighten each page by rotating it to the correct angle. This process is called "deskewing".
Note that the automatic processing will sometimes fail. It is always a good idea to manually control the results of unpaper and adjust the parameter settings according to the requirements of the input. Each processing step can also be disabled individually for each sheet.
Input and output files can be in either .pbm, .pgm or .ppm format, thus
generally in .pnm format, as also used by the Linux scanning tools scanimage
and scanadf.
Conversion to PDF can e.g. be achieved with the Linux tools pgm2tiff, tiffcp
and tiff2pdf.
Licensed under GNU GPL v2 — see COPYING for more information.