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Some input PDFs with Tesseract-OCR throw error in PyPDF2.utils.PdfReadError(Unexpected escaped string: b'{')' raised in ... #2
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There's an error in the PDF file. I run qpdf to try to fix errors before anything else, but it can't fix everything. You could "re-fry" the PDF with ghostscript, which rewrites and hopefully fixes the error. This has other side effects.
Can you provide a link to a sample? (Dropbox, etc.) |
@jbarlow83 Give me some time, I will try to find what went wrong (the scanned PDF was produced with gscan2pdf and tesseract. Perhaps I used already pdftk to merge some parts, and this step introduced the problem). My own project (not published yet) creates single pages from a multi-page input pdf, converts them to single lossless-compressed images (png, not using convert but ghostscript), tesseract-ocrs (pdf rendering mode) page-by-page, and then uses pdftk to concatenate (re-merge) the single pages to the multi-page, double-layer output pdf. In that way, pdf errors are almost never coming up. |
I'd like the PDF because any errors get added to the test suite. I'm less interested in what produced the problem so much as trying to make sure all readable PDFs are accepted even if they are invalid. Your project is quite similar to what this one does right now - just so you're aware. ocrmypdf converts pages to PNG uses ghostscript (btw: ImageMagick's convert also uses ghostscript, it just uses it badly), then uses tesseract for PDF rendering (optional with Tesseract's PDF rendering has some issues (at least as of 3.03). It gets DPI wrong, it produces PDFs with syntax errors, and it can inflate file size in some situations. For those reasons |
re. ghostscript vs. convert, yes, you are fully right. See http://bertanguven.com/faster-conversions-from-pdf-to-pngjpeg-imagemagick-vs-ghostscript/ . And thanks for all the other infos. BTW, I helped the tesseract people to fix a problem with the re-compression of the image (and I am proud, because it was difficult for some days). For a certain period, they lossy-re-compressed the input image (because the design goal was then to create minimal file sizes, which is a wrong goal), which introduced coding artefacts. This is fixed since about one year, and current tesseract version are coding very well. When you now say, that Tesseract introduces PDF syntax errors, this explains my current issue. Thanks for info. Please, if you have further information why or when Tesseracts creates wrong PDFs, pls. report your observations upstream. They (user zdenop) will fix the issue. Just for your information: From my script the line where a pdf page is losslessy converted to an image (which is then input to tesseract, and rendered to pdf):
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This is a Doublure of #19 . |
Mon Sep 7 18:56:47 2015
Originally opened as fritz-hh/OCRmyPDF#120
A few PDF input files (which were already processed by tesseract-ocr pdf mode) throw an error in OCRmyPDF even in the
--force-ocr
mode. At the moment, I have no idea what exactly happens, but the problem appears to be in PyPDF2 (I use PyPDF2 1.25.1).The error message is only shown when OCRmyPDF is used with the
-v
option.Do you have an idea what went wrong in these cases, or what else can be done to let OCRmyPDF apply another OCR run to such a PDF?
Full output:
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