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Joint Photographic Experts Group Compression (JPEG)

ISO and CCITT working committee joint together and formed Joint Photographic
Experts Group. It is focused exclusively on still image compression.
Another joint committee, known as the Motion Picture Experts Group (MPEG),
is concerned with full motion video standards.
JPEG is a compression standard for still color images and grayscale images,
otherwise known as continuous tone images

JPEG has been released as an ISO standard in two parts:

o specifies the modes of operation, the interchange formats, and the
encoder/decoder specifies for these modes along with substantial
implementation guide lines.
o describes compliance tests which determine whether the implementation
of an encoder or decoder conforms to the standard specification of part I to
ensure interoperability of systems compliant with JPEG standards.

Requirements addressed by JPEG

o The design should address image quality
o The compression standard should be applicable to practically any kind of
continuous-tone digital source image
o It should be scalable from completely lossless to lossy ranges to adapt it.
o It should provide sequential encoding
o It should provide for progressive encoding
o It should also provide for hierarchical encoding
o The compression standard should provide the option of lossless encoding
so that images can be guaranteed to provide full detail at the selected
resolution when decompressed

Definitions in the JPEG Standard

The JPEG Standards have three levels of definition as follows:

 Base line system
 Extended system
 Special lossless function.

The base line system must reasonably decompress color images, maintain a high
compression ratio, and handle from 4 bits/pixel to 16 bits/pixel.

The extended system covers the various encoding aspects such as variable-length
encoding, progressive encoding, and the hierarchical mode of encoding.