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unpaper 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). unpaper 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 disaligned 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.
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