Automatically restoring verticality of the edges of a scanned photo

Question

I want to scan a collection of rectangular photos, both color and black-and-white. I am generally quite happy with the scanning, but I run into some practical problems, due to the fact that photos are placed by hand and may not be well aligned with the scanning canvas (or the edges of the scanner)

I assume that my photo has been scanned into a white background rectangle containing the rectangular picture I want, possibly not aligned with the edge of the white rectangle.

Is there an application (preferably running on Linux) that can rotate automatically the scan so that the picture edges are horizontal/vertical? If it also crop out the surrounding white background, it is even better (though proper Unix design would separate this issue).

I know how to do that by hand with Gimp, checking the rotation with my eyes. But I would like to have it done automatically.

To make things clearer with actual images: given the first image below with the irregular white border, I would like to automatically extract the second one, without any surrounding white.

             

Note: I had to add the dashed-line to show the edges of the first image. If you want to test a proposed solution for the automatic extraction, you should rather use this image.

Answer 1

Sounds like you're looking for ImageMagick. This is typically installed by default with a lot of the more popular distros. If not you can use your distros package manager to install it.

Normal image rotation

$ sudo yum install ImageMagick

-or-

$ sudo apt-get install ImageMagick

ImageMagick includes many CLI tools, one of which is convert. Using convert you can rotate images like so:

$ convert -rotate "90" in.jpg out.jpg

There are many more examples on using convert here. The rest of the tools included with ImageMagick can do image editing, scaling, and annotating.

Deskewing

The other method for rotating images that are typically off a bit vertically or horizontally is called deskewing.

From the ImageMagick online command line options help:

-deskew threshold{%}
straighten an image. A threshold of 40% works for most images.

Use -set option:deskew:auto-crop true | false to auto crop the image.

To use this option, you'd use the convert CLI tool that's another of ImageMagicks CLI tools:

 $ convert skewed.jpeg -deskew 40% not_skewed.jpg

References

• List of ImageMagick CLI tools
• How to deskew a scanned text-page with ImageMagick?

Answer 2

I recently needed to digitalize the set of more than 500 photos made by film cameras. And needed to auto-trim and auto-rotate all of them.

Those parameters that worked better for me:

convert myFile.jpg -fuzz 30% -trim +repage -deskew 40% cropped_file.jpg

And here if you want to apply it to the entire folder:

mkdir cropped
for i in `ls *.JPG`; do convert $i -fuzz 30% -trim +repage -deskew 40% cropped/`basename $i JPG`jpg; done