2022-07-28 01:06:46 -07:00
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.. SPDX-FileCopyrightText: 2022 James R. Barlow
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..
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.. SPDX-License-Identifier: CC-BY-SA-4.0
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2018-08-27 01:25:30 -07:00
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.. _jbig2:
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2019-06-22 17:29:26 -07:00
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============================
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2018-08-09 21:14:50 -07:00
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Installing the JBIG2 encoder
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2018-08-27 01:25:30 -07:00
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============================
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2018-08-03 12:47:25 -07:00
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2019-06-22 17:29:26 -07:00
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Most Linux distributions do not include a JBIG2 encoder since JBIG2
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encoding was patented for a long time. All known JBIG2 US patents have
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expired as of 2017, but it is possible that unknown patents exist.
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2018-08-03 12:47:25 -07:00
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2019-06-22 17:29:26 -07:00
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JBIG2 encoding is recommended for OCRmyPDF and is used to losslessly
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2021-08-15 05:05:27 +02:00
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create smaller PDFs. If JBIG2 encoding is not available, lower quality
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encodings will be used.
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2018-08-03 12:47:25 -07:00
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2019-06-22 17:29:26 -07:00
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JBIG2 decoding is not patented and is performed automatically by most
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2021-08-15 05:05:27 +02:00
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PDF viewers. It is widely supported and has been part of the PDF
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specification since 2001.
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2019-06-22 17:29:26 -07:00
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On macOS, Homebrew packages jbig2enc and OCRmyPDF includes it by
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default. The Docker image for OCRmyPDF also builds its own JBIG2 encoder
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from source.
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2018-08-03 12:47:25 -07:00
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For all other Linux, you must build a JBIG2 encoder from source:
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.. code-block:: bash
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2019-06-22 17:29:26 -07:00
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git clone https://github.com/agl/jbig2enc
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cd jbig2enc
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./autogen.sh
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./configure && make
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[sudo] make install
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2018-10-04 01:31:53 -07:00
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.. _jbig2-lossy:
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2022-07-12 02:18:17 -07:00
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Dependencies include libtoolize and libleptonica, which on Ubuntu systems
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2022-04-05 00:25:28 -07:00
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are packaged as libtool and libleptonica-dev.
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2018-10-04 01:31:53 -07:00
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Lossy mode JBIG2
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================
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OCRmyPDF provides lossy mode JBIG2 as an advanced feature. Users should
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`review the technical concerns with JBIG2 in lossy
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mode <https://en.wikipedia.org/wiki/JBIG2#Disadvantages>`__
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and decide if this feature is acceptable for their use case.
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JBIG2 lossy mode does achieve higher compression ratios than any other
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monochrome (bitonal) compression technology; for large text documents
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the savings are considerable. JBIG2 lossless still gives great
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compression ratios and is a major improvement over the older CCITT G4
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standard. As explained above, there is some risk of substitution errors.
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To turn on JBIG2 lossy mode, add the argument ``--jbig2-lossy``.
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``--optimize {1,2,3}`` are necessary for the argument to take effect
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also required. Also, a JBIG2 encoder must be installed as described in
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the previous section.
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*Due to an oversight, ocrmypdf v7.0 and v7.1 used lossy mode by
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default.*
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