TurboJPEG Java Wrapper

======================

The TurboJPEG shared library can optionally be built with a Java Native

Interface wrapper, which allows the library to be loaded and used directly from

Java applications.  The Java front end for this is defined in several classes

located under org/libjpegturbo/turbojpeg.  The source code for these Java

classes is licensed under a BSD-style license, so the files can be incorporated

directly into both open source and proprietary projects without restriction.  A

Java archive (JAR) file containing these classes is also shipped with the

"official" distribution packages of libjpeg-turbo.

TJExample.java, which should also be located in the same directory as this

README file, demonstrates how to use the TurboJPEG Java API to compress and

decompress JPEG images in memory.

Performance Pitfalls

--------------------

The TurboJPEG Java API defines several convenience methods that can allocate

image buffers or instantiate classes to hold the result of compress,

decompress, or transform operations.  However, if you use these methods, then

be mindful of the amount of new data you are creating on the heap.  It may be

necessary to manually invoke the garbage collector to prevent heap exhaustion

or to prevent performance degradation.  Background garbage collection can kill

performance, particularly in a multi-threaded environment (Java pauses all

threads when the GC runs.)

The TurboJPEG Java API always gives you the option of pre-allocating your own

source and destination buffers, which allows you to re-use those buffers for

compressing/decompressing multiple images.  If the image sequence you are

compressing or decompressing consists of images of the same size, then

pre-allocating the buffers is recommended.

Installation Directory

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The TurboJPEG Java Wrapper will look for the TurboJPEG JNI library

(libturbojpeg.so, libturbojpeg.jnilib, or turbojpeg.dll) in the system library

paths or in any paths specified in LD_LIBRARY_PATH (Un*x), DYLD_LIBRARY_PATH

(Mac), or PATH (Windows.)  Failing this, on Un*x and Mac systems, the wrapper

will look for the JNI library under the library directory configured when

libjpeg-turbo was built.  If that library directory is

/opt/libjpeg-turbo/lib32, then /opt/libjpeg-turbo/lib64 is also searched, and

vice versa.

If you installed the JNI library into another directory, then you will need

to pass an argument of -Djava.library.path={path_to_JNI_library} to java, or

manipulate LD_LIBRARY_PATH, DYLD_LIBRARY_PATH, or PATH to include the directory

containing the JNI library.