2018-08-27 01:25:30 -07:00
|
|
|
.. _jbig2:
|
|
|
|
|
|
2019-06-22 17:29:26 -07:00
|
|
|
============================
|
2018-08-09 21:14:50 -07:00
|
|
|
Installing the JBIG2 encoder
|
2018-08-27 01:25:30 -07:00
|
|
|
============================
|
2018-08-03 12:47:25 -07:00
|
|
|
|
2019-06-22 17:29:26 -07:00
|
|
|
Most Linux distributions do not include a JBIG2 encoder since JBIG2
|
|
|
|
|
encoding was patented for a long time. All known JBIG2 US patents have
|
|
|
|
|
expired as of 2017, but it is possible that unknown patents exist.
|
2018-08-03 12:47:25 -07:00
|
|
|
|
2019-06-22 17:29:26 -07:00
|
|
|
JBIG2 encoding is recommended for OCRmyPDF and is used to losslessly
|
|
|
|
|
create smaller PDFs. If JBIG2 encoding not available, lower quality
|
|
|
|
|
encodings will be used.
|
2018-08-03 12:47:25 -07:00
|
|
|
|
2019-06-22 17:29:26 -07:00
|
|
|
JBIG2 decoding is not patented and is performed automatically by most
|
|
|
|
|
PDF viewers. It is widely supported has been part of the PDF
|
|
|
|
|
specification since 2001.
|
2018-08-03 12:47:25 -07:00
|
|
|
|
2019-06-22 17:29:26 -07:00
|
|
|
On macOS, Homebrew packages jbig2enc and OCRmyPDF includes it by
|
|
|
|
|
default. The Docker image for OCRmyPDF also builds its own JBIG2 encoder
|
|
|
|
|
from source.
|
2018-08-03 12:47:25 -07:00
|
|
|
|
|
|
|
|
For all other Linux, you must build a JBIG2 encoder from source:
|
|
|
|
|
|
|
|
|
|
.. code-block:: bash
|
|
|
|
|
|
2019-06-22 17:29:26 -07:00
|
|
|
git clone https://github.com/agl/jbig2enc
|
|
|
|
|
cd jbig2enc
|
|
|
|
|
./autogen.sh
|
|
|
|
|
./configure && make
|
|
|
|
|
[sudo] make install
|
2018-10-04 01:31:53 -07:00
|
|
|
|
|
|
|
|
.. _jbig2-lossy:
|
|
|
|
|
|
|
|
|
|
Lossy mode JBIG2
|
2019-06-22 17:29:26 -07:00
|
|
|
================
|
|
|
|
|
|
|
|
|
|
OCRmyPDF provides lossy mode JBIG2 as an advanced feature. Users should
|
|
|
|
|
`review the technical concerns with JBIG2 in lossy
|
|
|
|
|
mode <https://abbyy.technology/en:kb:tip:jbig2_compression_and_ocr>`__
|
|
|
|
|
and decide if this feature is acceptable for their use case.
|
|
|
|
|
|
|
|
|
|
JBIG2 lossy mode does achieve higher compression ratios than any other
|
|
|
|
|
monochrome (bitonal) compression technology; for large text documents
|
|
|
|
|
the savings are considerable. JBIG2 lossless still gives great
|
|
|
|
|
compression ratios and is a major improvement over the older CCITT G4
|
|
|
|
|
standard. As explained above, there is some risk of substitution errors.
|
|
|
|
|
|
|
|
|
|
To turn on JBIG2 lossy mode, add the argument ``--jbig2-lossy``.
|
|
|
|
|
``--optimize {1,2,3}`` are necessary for the argument to take effect
|
|
|
|
|
also required. Also, a JBIG2 encoder must be installed as described in
|
|
|
|
|
the previous section.
|
|
|
|
|
|
|
|
|
|
*Due to an oversight, ocrmypdf v7.0 and v7.1 used lossy mode by
|
|
|
|
|
default.*
|
