I have scanned about 80 pages into gray scale pdf (image format). The end size of the file is about 70MB, which is very huge.
Now I am looking for a method to convert the grayscale image-based PDF file into a simple black/white text-based PDF file.
I have done many attempts with gs but with no success (only a few percent recovery).
If any expert has some idea, kindly let me know.
gImageReader is a simple GTK+ front-end to tesseract-ocr.
sudo apt-get install gimagereader tesseract-ocr
sorry for the german text
You can try pdfocr:
sudo add-apt-repository ppa:gezakovacs/pdfocr
sudo apt-get update
sudo apt-get install pdfocr
To execute the syntax is
pdfocr -i input.pdf -o output.pdf
where input.pdf is the name of the input file and output.pdf the output file.
By default it uses Tesseract. To install it:
sudo apt-get install tesseract-ocr
pdfocr creates an embedded text layer.
pdfsandwich
It loads tesseract and others on install. It's an easy one step solution and can be scripted. It can use hocr2pdf to create a plain text pdf, but its not ready for prime time...yet. The default uses tesseract and creates a "sandwiched" pdf: image + text underneath.
The embedded image can be removed with commands like:
gs -o ocr_noIMG.pdf -sDEVICE=pdfwrite -dFILTERIMAGE ocr_image.pdf
but the text is hidden, so it looks like a blank page.
Loading the PDF into LibreOffice Draw exposes the text and the image can be deleted manually.
I came across this question whilst looking to convert a scanned PDF to a text-selectable PDF. I later found pdfsandwich which I have had very good results with and I am surprised isn't featured in detail, in the answers so far.
More information is available here: http://www.tobias-elze.de/pdfsandwich/
It uses the Google-sponsored tesseract optical character recognition library behind the scenes but simplifies the PDF processing and creation steps.
As of December 2020, it is included in the official Ubuntu repositories. To install:
sudo apt update && sudo apt install pdfsandwich
To process a PDF called input.pdf:
pdfsandwich input.pdf
By default, your output will appear as something like input_ocr.pdf
On Ubuntu 20.04, it didn't work initially due to a Ghostscript permissions issue. This can be worked around by adding XML comments (<!-- xxx -->) around out the following lines in /etc/ImageMagick-6/policy.xml (in my file, these were lines 90 - 95):
<policy domain="coder" rights="none" pattern="PS" />
<policy domain="coder" rights="none" pattern="PS2" />
<policy domain="coder" rights="none" pattern="PS3" />
<policy domain="coder" rights="none" pattern="EPS" />
<policy domain="coder" rights="none" pattern="PDF" />
<policy domain="coder" rights="none" pattern="XPS" />
Reference for this fix: https://www.itechlounge.net/2020/09/web-imagickexception-attempt-to-perform-an-operation-not-allowed-by-the-security-policy-pdf/
To read the documentation:
man pdfsandwich
If your document is not English, you can add the -lang switch like this:
pdfsandwich -lang xxx input.pdf
where xxx is the language of the document you need to convert. Note that, if not present, you need to install additional language support using:
sudo apt install tesseract-ocr-xxx
For the graphical interface suggested by @A.B. on ubuntu 14.04 you should follow:
or anyway, add to the repository list:
sudo add-apt-repository ppa:sandromani/gimagereader
sudo apt-get update
before this works:
sudo apt-get install gimagereader
Actually the best I've found is the command pdftotext
sudo apt install poppler-utils
pretty slick and simple if you do pdftotext -layout xxx.pdf you even get the original layout preserved as text.
