Overview of JPEG

The JPEG standard (ISO/IEC 10918) was created in 1992 (latest version, 1994) as the result of a process that started in 1986. Though, this standard is generally considered as a single specification, in reality it is composed of four separate parts and an amalgam of coding modes.

Part 1 of JPEG (ISO/IEC 10918-1 | ITU-T Recommendation T.81) specifies the core coding technology and it incorporates many options for encoding photographic images. Part 2 defines the compliance testing. Part 3 defines a set of extensions to the coding technologies of Part 1, and via an amendment the SPIFF file format was introduced. Part 4 focuses on the registration of JPEG profiles, SPIFF profiles, SPIFF tags, SPIFF color spaces, SPIFF compression types, and defines the Registration Authorities. And lastly, Part 5 specifies the JPEG File Interchange Format (JFIF). Without any doubt, it can be stated that JPEG has been one of the most successful multimedia standards defined so far.

While JPEG (Rec. ITU T.81 | ISO/IEC 10918) is still the most dominant still image format around, it may seem surprising that ISO/IEC never provided a reference software demonstrating a proper implementation of the standard. Therefore, JPEG initiated an initiative to create a new reference implementation for ISO/IEC 10918. More information on the call can be found here.

JPEG currently includes the following parts:

Part 1: Requirements and guidelines

Specifies the core coding system, consisting of the well-known Huffman-coded DCT based lossy image format, but also including the arithmetic coding option, lossless coding and hierarchical coding.

Part 2: Compliance testing

Specifies conformance testing, and as such provides test procedures and test data to test JPEG encoders and decoders for conformance.

Part 3: Extensions

Specifies various extensions of the JPEG format, as such spatially variable quantization, tiling, selective refinement and the SPIFF file format.

Part 4: Registration authorities

Registers known application markers, SPIFF tags profiles, compression types and registration authorities.

Part 5: File Interchange Format

Specifies the JPEG File Interchange Format (JFIF) which includes the chroma upsampling and YCbCr to RGB transformation.

Part 6: Application to printing systems

Specifies markers that refine the colour space interpretation of JPEG codestreams, such as to enable the embedding of ICC profiles and to allow the encoding in the CMYK colour model.

Part 7: Reference Software

Provides JPEG Reference Software implementations.