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Recompressing the source png files caused the output test files to be
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Proper grayscale tests and golden files should actually be added, but
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tests tests: update golden files to reflect the actual output filetype.
.dir-locals.el Update README with build information. Add auto-fill-mode to MarkDown.
.gitignore add compare-image binary
.mailmap git: add a mailmap to make Jens's commits look nicer.
AUTHORS Replaced interpolation functions for better image quality.
COPYING Rename files to follow autotools style more closely. Remove explicit rule for tests/.dirstamp.
NEWS Update version information and NEWS file for the next release. Update documentation about file formats. Update version information and NEWS file for the next release.
file.c Destroy (most) of the libav data structures created during file loadi…
imageprocess.c Consistently reduce to single precision floating point the rotation c…
imageprocess.h Use float rather than double for rotation detection.
parse.c Move mask checking into imageprocess.c as inline.
parse.h Move mask checking into imageprocess.c as inline.
tools.c Remove unused function.
tools.h Remove unused function.
unpaper.1.xml Move the local variables settings for nxml to .dir-locals.
unpaper.c fix a possible printf(NULL) when -debug is used
unpaper.h Use float for the degrees-to-radians conversion, too.


Originally written by Jens Gulden — see AUTHORS for more information. Licensed under GNU GPL v2 — see COPYING for more information.


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 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.

See further documentation for the supported file formats notes.


The only hard dependency of unpaper is libav, which is used for file input and output.

At the time of writing, any version of libav can be used, and at least from version 9 it supports a superset of the file formats supported by unpaper before version 6.

The yet to be released version 11 is recommended, once available, as it has better support for TIFF files, including a faster, less memory-consuming support for grayscale TIFF files, and support for grayscale and alpha files.

Building instructions

unpaper uses GNU Autotools for its build system, so you should be able to execute the same commands used for other software packages:

sudo make install

There are, though, some recommendations about the way you build the code. Since the tasks are calculation-intensive, it is important to build with optimizations turned on:

./configure CFLAGS="-O2 -march-native -pipe"

Even better, if your compiler supports it, is to use Link-Time Optimizations, as that has shown that execution time can improve sensibly:

./configure CFLAGS="-O2 -march=native -pipe -flto"

Further optimizations such as -ftracer and -ftree-vectorize are thought to work, but their effect has not been evaluated so your mileage may vary.

Further Information

You can find more information on the basic concepts and the image processing in the available documentation.

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