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Describe how to use tesseract 4.0 while 3.04 is installed

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James R. Barlow
2017-01-27 18:13:59 -08:00
parent 99afebd033
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@@ -130,13 +130,37 @@ Image processing commands can be combined. The order in which options are given
Control of OCR options
----------------------
By default, OCRmyPDF permits tesseract to run for only three minutes (180 seconds) per page. This is usually more than enough time to find all text on a reasonably sized page with modern hardware. A skipped page will be inserted into the output without any OCR text.
OCRmyPDF provides many features to control the behavior of the OCR engine, Tesseract.
If you want to adjust the amount of time spent on OCR, change ``--tesseract-timeout``. You can also automatically skip images that exceed a certain number of megapixels.
Time and image size limits
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By default, OCRmyPDF permits tesseract to run for only three minutes (180 seconds) per page. This is usually more than enough time to find all text on a reasonably sized page with modern hardware.
If a page is skipped, it will be inserted without OCR. If preprocessing was requested, the preprocessed image layer will be inserted.
If you want to adjust the amount of time spent on OCR, change ``--tesseract-timeout``. You can also automatically skip images that exceed a certain number of megapixels. (A 300 DPI, 8.5×11" page is 8.4 megapixels.)
.. code-block:: bash
# Allow 300 seconds for OCR; skip any page larger than 50 megapixels
ocrmypdf --tesseract-timeout 300 --skip-big 50 bigfile.pdf output.pdf
Overriding default tesseract
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OCRmyPDF checks the environment variable ``OCRMYPDF_TESSERACT`` for the full path to the tesseract executable first.
For example, if you are testing tesseract 4.00 and don't wish to disturb your tesseract 3.04 installation, you can launch OCRmyPDF as follows:
.. code-block:: bash
env \
OCRMYPDF_TESSERACT=/home/user/src/tesseract4/api/tesseract \
TESSDATA_PREFIX=/home/user/src/tesseract4 \
ocrmypdf --pdf-renderer tess4 --tesseract-oem 2 input.pdf output.pdf
* ``TESSDATA_PREFIX`` directs tesseract 4.0 to use LSTM training data. This is a tesseract environment variable.
* ``--pdf-renderer tess4`` takes advantage of new tesseract 4.0 PDF renderer in OCRmyPDF. (Tesseract 4.0 only.)
* ``--tesseract-oem 2`` requests tesseract 4.0's new LSTM engine. (Tesseract 4.0 only.)