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https://issues.apache.org/jira/browse/TIKA-93?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13896339#comment-13896339
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Timo Boehme commented on TIKA-93:
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I would like to give some comments on detecting/handling of image based PDFs
because the proposed solution will only work with a subset of these kind of
documents. First one could classify the image based PDF into 3 classes:
# image only (one image per page)
# image with text overlay/underlay already produced by an OCR process
# multiple images per page (instead of one full page image there are images per
word/line/paragraph)
Thus from only testing for a page size image one does not known if we
nevertheless have parseable text or if we have a class 3 document (in case of
e.g. journals we might even have a full page background image). For an
automatic classification one would need to first try to parse text in the
standard way for a view pages. One should not expect image-only PDFs to contain
no text - in some cases header/footer/page numbers are added as text whereas
other content is only an image. An heuristic threshold are 60-80 characters per
page below which we can assume to have an image PDF.
If a PDF is assumed to be an image PDF the pages should be 'printed' into an
image (in order to also handle class 3 documents and to keep mixed data (image
+ text)) and this image should be processed by OCR.
Best,
Timo
> OCR support
> -----------
>
> Key: TIKA-93
> URL: https://issues.apache.org/jira/browse/TIKA-93
> Project: Tika
> Issue Type: New Feature
> Components: parser
> Reporter: Jukka Zitting
> Assignee: Chris A. Mattmann
> Priority: Minor
> Attachments: TIKA-93.patch, TIKA-93.patch, TIKA-93.patch,
> TIKA-93.patch, testOCR.docx, testOCR.pdf, testOCR.pptx
>
>
> I don't know of any decent open source pure Java OCR libraries, but there are
> command line OCR tools like Tesseract
> (http://code.google.com/p/tesseract-ocr/) that could be invoked by Tika to
> extract text content (where available) from image files.
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