A simple tool to fix images. Usually, scanned images are
- slightly (or quite) rotated
- have a background around the page or photo
The autorotate command line tool
- trims away a background color
- looks for straight edges at the right, left, top and bottom
- rotates and trims the image
- saves it to a file, converting the format as necessary
autorotate is written in Haskell, but relies heavily on the ImageMagick library.
Tested on
- Fedora 20 with ghc (7.6.3) and ImageMagick 6.8.6.3
- Ubuntu 16.04 with ghc (7.10.3) and ImageMagick 6.8.0.0
Fedora:
yum install ImageMagick ImageMagick-devel ImageMagick-libs
Ubuntu:
sudo apt-get install imagemagick libmagic++-dev cabal-install
cabal install
$ autorotate in-file.png out-file.png
There are some command line switches. Read Main.hs or try
$ autorotate --help
Rotation angle is determined by looking at the slopes of lines connecting all combinations of edge points along each edge. The most frequent values are averaged, resulting in a highly accurate angle. Since all four edges are detected, even torn pages and folded corners get handled so long as there are some straight, perpendicular lines along the perimeter.
The algorithm is not especially efficient, and takes as long as the rotation and trimming operations.