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Hash : 94c64ead
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Date : 2024-06-17T20:27:57
Various doc tweaks - "bits per component" = "bits per sample" Describing the data precision of a JPEG image using "bits per component" is technically correct, but "bits per sample" is the terminology that the JPEG-1 spec uses. Also, "bits per component" is more commonly used to describe the precision of packed-pixel formats (as opposed to "bits per pixel") rather than planar formats, in which all components are grouped together. - Unmention legacy display technologies. Colormapped and monochrome displays aren't a thing anymore, and even when they were still a thing, it was possible to display full-color images to them. In 1991, when JPEG decompression time was measured in minutes per megapixel, it made sense to keep a decompressed copy of JPEG images on disk, in a format that could be displayed without further color conversion (since color conversion was slow and memory-intensive.) In 2024, JPEG decompression time is measured in milliseconds per megapixel, and color conversion is even faster. Thus, JPEG images can be decompressed, displayed, and color-converted (if necessary) "on the fly" at speeds too fast for human vision to perceive. (In fact, your TV performs much more complicated decompression algorithms at least 60 times per second.) - Document that color quantization (and associated features), GIF input/output, Targa input/output, and OS/2 BMP input/output are legacy features. Legacy status doesn't necessarily mean that the features are deprecated. Rather, it is meant to discourage users from using features that may be of little or no benefit on modern machines (such as low-quality modes that had significant performance advantages in the early 1990s but no longer do) and that are maintained on a break/fix basis only. - General wordsmithing, grammar/punctuation policing, and formatting tweaks - Clarify which data precisions each cjpeg input format and each djpeg output format supports. - cjpeg.1: Remove unnecessary and impolitic statement about the -targa switch. - Adjust or remove performance claims to reflect the fact that: * On modern machines, the djpeg "-fast" switch has a negligible effect on performance. * There is a measurable difference between the performance of Floyd- Steinberg dithering and no dithering, but it is not likely perceptible to most users. * There is a measurable difference between the performance of 1-pass and 2-pass color quantization, but it is not likely perceptible to most users. * There is a measurable difference between the performance of full-color and grayscale output when decompressing a full-color JPEG image, but it is not likely perceptible to most users. * IDCT scaling does not necessarily improve performance. (It generally does if the scaling factor is <= 1/2 and generally doesn't if the scaling factor is > 1/2, at least on my machine. The performance claim made in jpeg-6b was probably invalidated when we merged the additional scaling factors from jpeg-7.) - Clarify which djpeg switches/output formats cannot be used when decompressing lossless JPEG images. - Remove djpeg hints, since those involve quality vs. speed tradeoffs that are no longer relevant for modern machines. - Remove documentation regarding using color quantization with 16-bit data precision. (Color quantization requires lossy mode.) - Java: Fix typos in TJDecompressor.decompress12() and TJDecompressor.decompress16() documentation. - jpegtran.1: Fix truncated paragraph In a man page, a single quote at the start of a line is interpreted as a macro. Closes #775 - libjpeg.txt: * Mention J16SAMPLE data type (oversight.) * Remove statement about extending jdcolor.c. (libjpeg-turbo is not quite as DIY as libjpeg once was.) * Remove paragraph about tweaking the various typedefs in jmorecfg.h. It is no longer relevant for modern machines. * Remove caveat regarding systems with ints less than 16 bits wide. (ANSI/ISO C requires an int to be at least 16 bits wide, and libjpeg-turbo has never supported non-ANSI compilers.) - usage.txt: * Add copyright header. * Document cjpeg -icc, -memdst, -report, -strict, and -version switches. * Document djpeg -icc, -maxscans, -memsrc, -report, -skip, -crop, -strict, and -version switches. * Document jpegtran -icc, -maxscans, -report, -strict, and -version switches.
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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.