How To Scan to OCR From The Command Line
24 Oct 2011I just had to remind myself how to scan to OCR, and thought I would share the results.
Before you start, you need to have sane installed, and you also need tesseract-ocr - both should be available in your distros repositories.
$ sudo apt-get install sane-utils tesseract-ocr
Next you need to find out what scanners you have available, and you do this with:
$ scanimage -L
device `v4l:/dev/video0' is a Noname Vimicro USB Camera (Altair) virtual device
device `plustek:libusb:004:002' is a Epson Perfection 1250/Photo flatbed scanner)
Obviously the latter is my scanner.
Assuming you have a working scanner, the following is a simple two liner to scan and OCR.
$ scanimage -d 'plustek:libusb:004:002' --mode Lineart \
--format tiff -x 215 -y 297 --resolution 200 > example.tif
And finally convert to text with tesseract:
$ tesseract /tmp/example.tif example
You should now have a file example.txt in your current directory, which you can open in any text editor.
Obviously this has limitations - it works for single-page A4 portrait typed documents - but it gives you the basics.
You could probably experiment with the resolution, 200 worked for me, so I didn’t bother trying anything else.  Traditionally the higher the resolution the better, but I seem to recall that tesseract works better on 300 and below.
On my Epson Perfection 1250 I found that I needed to add the sane
switch --warmup-time 0 as otherwise it never finished warming up.
If you would prefer to OCR an existing PDF, which is another thing that I find myself doing from time to time, then first convert it to a tif:
$ convert -density 200 example.pdf -depth 8 /tmp/example.tif
And then run the above tesseract command.