PDFBox is capable of handing advanced image formats such as JPEG2000.
While the jar files related to these advanced capability are also open
source, they differ enough that they can not be bundled and shipped
with the default pdfbox.jar download.

PDFBox has been designed to notice if these extra jar files are part
of its class-path when run, and dynamically load in and use them.

This directory in the pdf-box extension for Greenstone is designed to
help with a user, who has installed Greenstone, to download the
advanced image processing jars (accepting them under their specific
software licences) and place them within the relevant lib/jar area
within Greenstone.

PDFConverterPlugin is coded to notice if these extra jars are present,
and if so, update the '-cp' class-path argument it uses when launching
pdfbox.jar.

For more details about the JPEG2000 extra jar, and further advanced
image formats/handling that could be included, see:

  https://pdfbox.apache.org/2.0/dependencies.html#optional-components

(relevant snippet below)

TLDR:
  ./DOWNLOAD-ADDITIONAL-JARS.sh


---
<snip>

  JAI Image I/O

  PDF supports embedded image files, however support for some formats
  require third party libraries which are distributed under terms
  incompatible with the Apache 2.0 license:

  Reading JBIG2 images: JBIG2 ImageIO
  Reading JPEG 2000 (JPX) images: JAI Image I/O Tools Core
  Writing TIFF images requires JAI Image I/O Tools Core also.

  These libraries are optional and will be loaded if present on the
  classpath, otherwise support for these image formats will be disabled
  and a warning will be logged when an unsupported image is
  encountered.

  Maven dependencies for these components can be found in
  parent/pom.xml. Change the scope of the components if needed. Please
  make sure that any third party licenses are suitable for your
  project.

  To include the JBIG2 library the following part can be included in
  your project pom.xml:

  <dependency>
      <groupId>org.apache.pdfbox</groupId>
      <artifactId>jbig2-imageio</artifactId>
      <version>...</version>
  </dependency>

  To include the JAI capabilities the following part can be included in
  your project pom.xml:

  <dependency>
      <groupId>com.github.jai-imageio</groupId>
      <artifactId>jai-imageio-core</artifactId>
      <version>...</version>
  </dependency>
  <dependency>
      <groupId>com.github.jai-imageio</groupId>
      <artifactId>jai-imageio-jpeg2000</artifactId>
      <version>...</version>
  </dependency>

  For more reliable JPEG decoding the following part from the
  TwelveMonkeys library can be included in your project pom.xml:

  <dependency>
      <groupId>com.twelvemonkeys.imageio</groupId>
      <artifactId>imageio-jpeg</artifactId>
      <version>...</version>
  </dependency>

</snip>
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