JBIG is a standard for lossless compression method of digital images. The abbreviation is an acronym of the editorial group Joint Bi-level Image Experts Group, which is part of the responsibility for the JPEG method undersigned Joint Photographic Experts Group. Its members include experts from various national standards organizations.

The image size is below the code ISO / IEC 11544 and published ITU -T Recommendation T.82. Meanwhile, a new two-step algorithm was developed and called JBIG2; the precursor is now called JBIG1. JBIG has been specially developed for binary images such as faxes, but can also be used for other images. Mostly it compresses 20% to 50 % better than the Group 4 fax standard in special cases, 30 times stronger.

JBIG uses a patented IBM algorithm called Q- coder ( arithmetic coding ). It is based on probability of each bit with respect to the previous bit and the preceding image line. To allow the compression and decompression of images in the scanning direction, the following bits are not considered. JBIG also supports the progressive image structure with additional data, enlarge the image file by about 5 %.