JBIG is a 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. 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 the Fax Group 4 standard, and in some situations, it offers a 30-fold improvement.
JBIG is based on a form of arithmetic coding patented by IBM, known as the Q-coder, but using a minor tweak patented by Mitsubishi, resulting in what became known as the QM-coder. It bases the probabilities of each bit on the previous bits and the previous lines of the picture. In order to allow compressing and decompressing images in scanning order, it does not reference future bits. JBIG also supports progressive transmission with small (around 5%) overheads.
Patent licence requirements for JBIG1 implementations by IBM, Mitsubishi and AT&T prevented the codec to become widely implemented in open-source software. For example, as of 2012, none of the commonly used web browsers supported it.
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 the submarine patent US5404140 in the United States (on 4 April 2012).
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