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Hash : 9a146f0f
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Date : 2023-01-06T10:29:10
TurboJPEG: Numerous documentation improvements - Wordsmithing, formatting, and grammar tweaks - Various clarifications and corrections, including specifying whether a particular buffer or image is used as a source or destination - Accommodate/mention features that were introduced since the API documentation was created. - For clarity, use "packed-pixel" to describe uncompressed source/destination images that are not planar YUV. - Use "row" rather than "line" to refer to a single horizontal group of pixels or component values, for consistency with the libjpeg API documentation. (libjpeg also uses "scanline", which is a more archaic term.) - Use "alignment" rather than "padding" to refer to the number of bytes by which a row's width is evenly divisible. This consistifies the documention of the YUV functions and tjLoadImage(). ("Padding" typically refers to the number of bytes added to each row, which is not the same thing.) - Remove all references to "the underlying codec." Although the TurboJPEG API originated as a cross-platform wrapper for the Intel Integrated Performance Primitives, Sun mediaLib, QuickTime, and libjpeg, none of those TurboJPEG implementations has been maintained since 2009. Nothing would prevent someone from implementing the TurboJPEG API without libjpeg-turbo, but such an implementation would not necessarily have an "underlying codec." (It could be fully self-contained.) - Use "destination image" rather than "output image", for consistency, or describe the type of image that will be output. - Avoid the term "image buffer" and instead use "byte buffer" to refer to buffers that will hold JPEG images, or describe the type of image that will be contained in the buffer. (The Java documentation doesn't use "byte buffer", because the buffer arrays literally have "byte" in front of them, and since Java doesn't have pointers, it is not possible for mere mortals to store any other type of data in those arrays.) - C: Use "unified" to describe YUV images stored in a single buffer, for consistency with the Java documentation. - Use "planar YUV" rather than "YUV planar". Is is our convention to describe images using {component layout} {colorspace/pixel format} {image function}, e.g. "packed-pixel RGB source image" or "planar YUV destination image." - C: Document the TurboJPEG API version in which a particular function or macro was introduced, and reorder the backward compatibility function stubs in turbojpeg.h alphabetically by API version. - C: Use Markdown rather than HTML tags, where possible, in the Doxygen comments.
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README
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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 ---------------------- The TurboJPEG Java Wrapper will look for the TurboJPEG JNI library (libturbojpeg.so, libturbojpeg.dylib, 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.