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52 lines
2.5 KiB
Text
52 lines
2.5 KiB
Text
TurboJPEG Java Wrapper
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======================
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The TurboJPEG shared library can optionally be built with a Java Native
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Interface wrapper, which allows the library to be loaded and used directly from
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Java applications. The Java front end for this is defined in several classes
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located under org/libjpegturbo/turbojpeg. The source code for these Java
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classes is licensed under a BSD-style license, so the files can be incorporated
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directly into both open source and proprietary projects without restriction. A
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Java archive (JAR) file containing these classes is also shipped with the
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"official" distribution packages of libjpeg-turbo.
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TJExample.java, which should also be located in the same directory as this
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README file, demonstrates how to use the TurboJPEG Java API to compress and
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decompress JPEG images in memory.
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Performance Pitfalls
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--------------------
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The TurboJPEG Java API defines several convenience methods that can allocate
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image buffers or instantiate classes to hold the result of compress,
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decompress, or transform operations. However, if you use these methods, then
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be mindful of the amount of new data you are creating on the heap. It may be
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necessary to manually invoke the garbage collector to prevent heap exhaustion
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or to prevent performance degradation. Background garbage collection can kill
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performance, particularly in a multi-threaded environment (Java pauses all
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threads when the GC runs.)
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The TurboJPEG Java API always gives you the option of pre-allocating your own
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source and destination buffers, which allows you to re-use those buffers for
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compressing/decompressing multiple images. If the image sequence you are
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compressing or decompressing consists of images of the same size, then
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pre-allocating the buffers is recommended.
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Installation Directory
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----------------------
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The TurboJPEG Java Wrapper will look for the TurboJPEG JNI library
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(libturbojpeg.so, libturbojpeg.jnilib, or turbojpeg.dll) in the system library
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paths or in any paths specified in LD_LIBRARY_PATH (Un*x), DYLD_LIBRARY_PATH
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(Mac), or PATH (Windows.) Failing this, on Un*x and Mac systems, the wrapper
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will look for the JNI library under the library directory configured when
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libjpeg-turbo was built. If that library directory is
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/opt/libjpeg-turbo/lib32, then /opt/libjpeg-turbo/lib64 is also searched, and
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vice versa.
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If you installed the JNI library into another directory, then you will need
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to pass an argument of -Djava.library.path={path_to_JNI_library} to java, or
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manipulate LD_LIBRARY_PATH, DYLD_LIBRARY_PATH, or PATH to include the directory
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containing the JNI library.
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