JBIG-KIT Highly effective data compression algorithm
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algorithm compression data compression algorithm decompression functions decompression

JBIG-KIT Description

Highly effective data compression algorithm JBIG-KIT implements a highly effective data compression algorithm for bi-level high-resolution images such as fax pages or scanned documents.The JBIG-KIT project provides a portable C library of compression and decompression functions with a documented interface that can easily be included into image or document processing software.In addition, JBIG-KIT provides ready-to-use compression and decompression programs with a simple command line interface (similar to the converters found in netpbm). It implements the specification ISO 11544 and ITU-T T.82, which is commonly referred to as the "JBIG1 standard".Special features of the JBIG-KIT implementation are:* Fully reentrant multithread-capable design, also suitable for use in embedded systems (no global or static variables, isolated malloc()/free() calls, etc.).* Capable of handling incomplete and growing JBIG1 data streams in order to allow earliest display of low resolution versions.* Capable of handling several incoming data streams simultaneously in one single process and task.* Especially designed with applications in mind that want to display incoming data as early as possible (e.g., similar to the way in which Netscape Navigator handles incoming GIF images).* Implements all JBIG1 features and options, including progressive and sequential encoding, multiple bit planes, user specified resolution reduction and deterministic prediction tables, adaptive template changes for optimal performance on half-tone images, deterministic prediction, typical prediction in lowest and differential layers, various stripe orderings, etc. Only the SEQ and HITOLO options are currently not supported by the decoder (they are normally never required, but could be added later in case of user requirements).* Suitable for fax applications, satisfies ITU-T T.85 profile starting from version 1.5* Efficient code, optimized utilization of 32-bit processor registers.* Very easy to use documented C library interface.* Included Gray code conversion routines for efficient encoding of grayscale images.* Ready-to-use pbmtojbg and jbgtopbm converters. Here are some key features of "JBIG-KIT": · Close to state-of-the-art lossless compression ratio for high resolution bi-level images. · About 1.1 to 1.5 times better compression ratio on typical scanned documents compared to G4 fax compression (ITU-T T.6), which has been the best compression algorithm for scanned documents available prior to JBIG1. · Up to 30 times better compression of scanned images with dithered images compared to G4 fax compression. · About 2 times better compression on typical 300 dpi documents compared to “gzip -9” on raw bitmaps. · About 3–4 times better compression than GIF on typical 300 dpi documents. · Even much better competitive compression results on computer generated images, which are free of scanning distortions. · JBIG1 supports hierarchical “progressive” encoding, meaning that it is possible to encode a low resolution image first, followed by resolution enhancement data, without adding a lot of redundancy. This allows, for instance, a document browser to display already a good 75 dpi low resolution version of an image, while the data necessary to reconstruct the full 300 dpi version for laser printer reproduction is still arriving (say over a slow network link or mass storage medium). · The various resolution layers of a JBIG1 image in progressive encoding mode combined require not much more space than a normal non-progressive mode encoded image (which JBIG1 also supports). · The progressive mode utilizes a sophisticated resolution-reduction algorithm to generate high-quality low resolution versions that preserve the shape of characters as well as the integrity of thin lines and dithered images. · JBIG1 supports multiple bit planes. Therefore, it can also be used for grayscale and color images. While its main field of application are bi-level images, that is images with only two different pixel values (black and white), JBIG1 has also been reported to perform better than JPEG’s original lossless mode on grayscale images that have up to 6 bits per pixel. Limitations: · The library was not designed for machine architectures with registers smaller than 32 bits (e.g., old MS-DOS C compilers, 8/16-bit microcontrollers or DSPs) on which a number of very efficient optimization techniques used in this software are not effective. For maximum performance, a 32-bit processor is required (64-bit systems work fine, too). On architectures with 16-bit pointer arithmetic, only very small images can be processed. What's New in This Release: · This major release adds a much more lightweight jbig85.c variant of the library that implements only the black/white fax profile (single bit per pixel, no progressive coding with multiple resolution layers) specified in ITU-T T.85. · It keeps only 3 lines of the uncompressed image in memory at any time, and only a few bytes of compressed data, and leaves all memory allocation to the caller. · This benefits in particular embedded low-memory applications, and those processing extremely large images. (There are also extensions to the original jbig.c library and its command-line tools.)

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