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Hash : 8456d2b9
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Date : 2024-08-30T10:50:13
Doc: "MCU block" = "iMCU" or "MCU" The JPEG-1 spec never uses the term "MCU block". That term is rarely used in other literature to describe the equivalent of an MCU in an interleaved JPEG image, but the libjpeg documentation uses "iMCU" to describe the same thing. "iMCU" is a better term, since the equivalent of an interleaved MCU can contain multiple DCT blocks (or samples in lossless mode) that are only grouped together if the image is interleaved. In the case of restart markers, "MCU block" was used in the libjpeg documentation instead of "MCU", but "MCU" is more accurate and less confusing. (The restart interval is literally in MCUs, where one MCU is one data unit in a non-interleaved JPEG image and multiple data units in a multi-component interleaved JPEG image.) In the case of 9b704f96b2dccc54363ad7a2fe8e378fc1a2893b, the issue was actually with progressive JPEG images exactly two DCT blocks wide, not two MCU blocks wide. This commit also defines "MCU" and "MCU row" in the description of the various restart marker options/parameters. Although an MCU row is technically always a row of samples in lossless mode, "sample row" was confusing, since it is used in other places to describe a row of samples for a single component (whereas an MCU row in a typical lossless JPEG image consists of a row of interleaved samples for all components.)
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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.