pdf -> searchable PDF

[Andreas Steibl]

Hello

I have a pdf (scanned) and now i make a searchable pdf from this

First i generate a black/white multipage tif, and with tesseract i can make a searchable pdf.

But is it somehow possible to integrate the original pdf images?

because the generated tif has not the same quality like the original (maybe the scaned image is in color)

[James R Barlow]

Tesseract cannot rasterize PDFs. It is fairly straightforward to write a PDF like does, but very complex to rasterize one.

Programs like OCRmyPDF (which I develop) use Ghostscript, Tesseract and other tools to handle PDF to searchable PDF conversion.

[ShreeDevi Kumar]

Please see https://github.com/tesseract-ocr/tesseract/issues/83 and other PDF related issues in GitHub repo with similar discussion.

- excuse the brevity, sent from mobile

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[wiki...@gmail.com]

Andreas,

we track your issue now as new issue https://github.com/tesseract-ocr/tesseract/issues/660 . Please don't miss to follow the discussion there.

It looks, as if the main developers are really interested in finding and implementing a solution (in which I am also very interested in.)

[Zdenko Podobný]

If pdf was created by scanner (there are only images pdf) I use something like this:

podofoimgextract test.pdf .

ls pdfimage_* >filelist

tesseract filelist searchable pdf

podofoimgextract is part of podofo project http://podofo.sourceforge.net/

Zdenko

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[Jeff Breidenbach]

There is a lengthy side discussion that is appropriate to move

back here. I've been asked to elaborate what I mean by image 

extraction.

  https://github.com/tesseract-ocr/tesseract/issues/660

There are two ways to turn a PDF file into images. One is to

render it, for example using a tool like pdftoppm. This is great

if there are things like fonts involved.

But far better, for bag-of-images PDF files, such as produced

by certain scanning machines, is to crack open the bag and

take out the images. This guarantees no rescaling, no loss

of image information, and no (possibly space inefficient) format 

conversions.

Tools for image extraction are not super common, but it sounds

from the name like podofoimgextract does it. And for a fairly limited

set of formats, so does pdfimages from poppler-utils. The best case

scenario is image extract with no transcoding whatsoever. That's

not always possible (expecially when dealing with really fancy formats

like JBIG2) but it should be fine for PDF files produced by a scanner.

And also any PDF files produced by Tesseract.