The Joint Photographic Expert Group (JPEG) was founded in 1986 by its parent bodies, the then ITU CCITT SG 8 and ISO/TC97/SC2/WG8 group. ITU-T Rec. T.81 | ISO/IEC 10918-1 specifies a process for digital compression and coding of continuous-tone still images, and is known as the “JPEG image compression scheme” that is pervasive today in the Internet, in digital photography and in many other image compression applications. Originally approved in 1992 jointly first by ITU-T (then CCITT) and later by ISO/IEC, the JPEG Committee went on after some years to define a newer family of image coding standards that has a significantly broader application scope than the original JPEG (namely still picture compression) and designed a broader “image architecture” – which is known as “JPEG2000” and is published in the ITU-T Rec. T.800 | ISO/IEC 15444 family of specifications. In the meantime, the immensely popular JPEG suite was not updated over time to exploit advances in image compression, even though it had been originally conceived as an expandable “tool box” concept.
Starting in 2004, ITU-T Study Group 16 consulted with ISO/IEC JTC1 SC29/WG 1 (the full name of the JPEG committee in ISO/IEC) about bringing into the original JPEG suite an alternative, royalty free arithmetic coder that would allow much better image compression efficiency and lower latency. Eventually it was decided by both groups that this would be an ITU-only extension of the base algorithm, and in order to distinguish it clearly from the original JPEG work, the specification was published after approval in September 2005 as ITU-T Rec. T.851 (“JPEG1-based still-image coding using an alternative arithmetic coder”).
From the onset of the development, there was the desire to have a freely available reference source code implementation of the alternative arithmetic coder in T.851. This work is now being coordinated between various experts aiming integration in the Independent JPEG Group distribution. Once stable, the code for the T.851 alternative arithmetic coder is planned to be formally approved as an Appendix to T.851, which could be easily updated as the source code is updated.