JBIG
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JBIG is an early lossless image compression standard from the Joint Bi-level Image Experts Group, standardized as ISO/IEC standard 11544 and as ITU-T recommendation T.82 in March 1993.<ref name="standards">Template:Cite book</ref> It is widely implemented in fax machines. Now that the newer bi-level image compression standard JBIG2 has been released, JBIG is also known as JBIG1. JBIG was designed for compression of binary images, particularly for faxes, but can also be used on other images. In most situations JBIG offers between a 20% and 50% increase in compression efficiency over Fax Group 4 compression, and in some situations, it offers a 30-fold improvement.
JBIG is based on a form of arithmetic coding developed by IBM (known as the Q-coder) that also uses a relatively minor refinement developed by Mitsubishi, resulting in what became known as the QM-coder. It bases the probability estimates for each encoded bit on the values of the previous bits and the values in previous lines of the picture. JBIG also supports progressive transmission, which generally incurs a small overhead in bit rate (around 5%).
PatentsEdit
Doubts about patent licence requirements for JBIG1 implementations by IBM, MitsuTemplate:Shybishi and AT&T prevented the codec from being widely implemented in open-source software.<ref name=Kuhn/> For example, as of 2012, none of the commonly used web browsers supported it. Since 2012, there are now no more JBIG1 patents in force – the last ones to expire were Mitsubishi's patents in Canada and Australia (on 25 February 2011) and in the United States (on 4 April 2012).<ref name=Kuhn>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
See alsoEdit
ReferencesEdit
External linksEdit
- JBIG-KIT – a free C implementation of the JBIG encoder and decoder
- ISO/IEC 11544
- ITU-T Recommendations T.82, T.85
- Template:IETF RFC – Content Feature Schema for Internet Fax (V2)
- Template:IETF RFC – File Format for Internet Fax
Template:ISO standards Template:List of International Electrotechnical Commission standards Template:Graphics file formats Template:Compression formats