1 line
3.6 KiB
Plaintext
1 line
3.6 KiB
Plaintext
CHANGE LOG for Independent JPEG Group's JPEG software
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Version 5alpha2 4-May-94
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-------------------------
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Two-pass color quantization is working, although it ought to be revisited
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to tune the algorithm for operation in RGB color space. The change to RGB
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means that the library can also quantize to an externally-supplied colormap;
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but I have not gotten around to implementing a djpeg switch for this.
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Output resizing via the IDCT works: see djpeg's "-scale" switch. The system
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design allows for more general rescaling at the upsample step, but I have no
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intention of implementing that anytime soon (any volunteers?).
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Other speed/quality tradeoff options remain to be implemented: alternate
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DCTs and merged color conversion/upsample/quantize are high on the list.
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Documentation is in fairly decent shape, although libjpeg.doc is still missing
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a few sections. All of the documentation will need updates as more features
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are added to v5.
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Version 5alpha1 6-Apr-94
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-------------------------
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This alpha-test release includes rewritten configuration/installation stuff.
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In particular there's now a "configure" script that should do everything
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needed for Unix installations. Please read install.doc.
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GIF and Targa file I/O are working again. Utah RLE is not there, and
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won't be unless someone volunteers to update those files.
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Huffman optimization and one-pass color quantization are working again.
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Two-pass quantization isn't fixed yet; ditto input smoothing and progress
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monitoring. Block smoothing is missing (and may remain so indefinitely...).
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Multiple-scan JPEG files are not supported for either encoding or decoding.
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None of the promised new v5 features (output resizing, speed/quality
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tradeoffs) are implemented yet.
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The documentation needs work; in particular, usage.doc/cjpeg.1/djpeg.1
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have not been updated. I have plans for an extensive "libjpeg.doc" file
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describing use of the library, but haven't written anything yet.
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Changes from version 4
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----------------------
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Version 5 represents a nearly complete redesign and rewrite of the IJG
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software. Major user-visible changes include:
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* Automatic configuration simplifies installation for most Unix systems.
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* A range of speed vs. image quality tradeoffs are [will be] supported.
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This includes resizing of an image during decompression: scaling down
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by a factor of 1/2, 1/4, or 1/8 is handled very efficiently.
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The application programmer's interface to the library has changed completely.
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Notable improvements include:
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* We have eliminated the use of callback routines for handling the
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uncompressed image data. The application now sees the library as a
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set of routines that it calls to read or write image data on a
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scanline-by-scanline basis.
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* The application image data is represented in a conventional interleaved-
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pixel format, rather than as a separate array for each color channel.
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This can save a copying step in many programs.
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* The handling of compressed data has been cleaned up: the application can
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supply routines to source or sink the compressed data. It is possible to
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suspend processing on source/sink buffer overrun, although this is not
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supported in all operating modes.
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* All static state has been eliminated from the library, so that multiple
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instances of compression or decompression can be active concurrently.
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* JPEG abbreviated datastream formats are supported, ie, quantization and
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Huffman tables can be stored separately from the image data.
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The last widely used release before the version 5 rewrite was version 4A of
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18-Feb-93. Change logs before that point have been discarded, since they
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are not of much interest after the rewrite.
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