Overview
ISO/IEC 14492:2019 (also published as ITU‑T Rec. T.88, commonly known as JBIG2) specifies methods for coding bi‑level images - images with a single bit plane (black & white). The standard supports lossless (bit‑preserving), lossy, and progressive coding of single images and multi‑page documents. It is particularly suited to pages containing text and dithered (halftone) data and also defines file formats to encapsulate the coded bi‑level image data.
Key topics and technical requirements
- Coding modes: Lossless, lossy, and lossy‑to‑lossless (progressive) coding options for bi‑level images.
- Region and page model: Support for different region types (text, halftone, generic, refinement) and multi‑page document composition.
- Symbol and pattern dictionaries: Methods to detect, encode and decode repeated symbols (e.g., glyphs) to improve compression for text and line art.
- Entropy coding: Support for arithmetic coding and Huffman tables (see Annex E and Annex B) to encode variable‑length data efficiently.
- Control and segments: Segment header and segment type structures that enable modular encoding and random access.
- File formats and organizations: Multiple file organization modes (sequential, random‑access, embedded) and a defined file header syntax (Annex D).
- Decoding/encoding procedures: Detailed procedures for decoding regions, control structures, and page make‑up; informative encoding guidance is also provided.
- Profiles and examples: Profiles, test data and compliant example methods are included (Annex F, Annex H, Annex J).
- IPR considerations: The standard notes potential patent claims and recommends consulting patent databases before implementation.
Applications and typical users
ISO/IEC 14492:2019 (JBIG2) is used where high‑efficiency compression of black‑and‑white documents is required:
- Document imaging and scanning software (archival scanners, document management systems)
- Enterprise content management and long‑term digital archives
- Fax and telecommunications systems that handle bi‑level pages
- OCR preprocessing and storage for text and mixed text/halftone pages
- Printing and reprographic workflows where compact storage of scanned pages is needed
Users implementing or selecting JBIG2 codecs include software developers, systems integrators, hardware OEMs (scanners, MFPs), standards and compliance engineers, and archivists focused on space‑efficient document storage.
Related standards
- ITU‑T Recommendation T.88 (same technical content)
- Other image coding standards for multi‑bit images (e.g., JPEG family) for comparison when grayscale or color is required.
Keywords: ISO/IEC 14492, JBIG2, bi‑level image compression, lossless image compression, lossy compression, progressive coding, symbol dictionary, arithmetic coding, Huffman, document imaging.