Overview
ISO/IEC 10918-3:1997 - also published as ITU‑T Rec. T.84 - defines extensions to the JPEG family for digital compression and coding of continuous‑tone still images (grayscale and colour). It standardizes additional coding processes, compressed data representations and a Still Picture Interchange File Format (SPIFF). The part complements ISO/IEC 10918‑1 (requirements) and ISO/IEC 10918‑2 (compliance testing), and includes normative annexes with mathematical definitions, file/marker formats and test procedures.
Key topics and requirements
- Extensions to JPEG coding: Defines optional mechanisms that extend baseline JPEG processes for improved flexibility and functionality.
- Variable quantization: Allows rescaling of quantizer values for AC DCT coefficients on a per‑8×8 block basis (see Annex C).
- Selective refinement: Provides rules for enhancing image regions after initial coding, including:
- Hierarchical selective refinement (refine by next differential frames)
- Progressive selective refinement (add coefficients or bits)
- Component selective refinement (refine a subset of colour components)
- Tiling: Multiple tiling models for large or multi‑resolution images:
- Simple tiling (contiguous non‑overlapping tiles)
- Composite tiling (overlapping tiles and collages)
- Pyramidal tiling (multi‑resolution pyramids)
- SPIFF (Still Picture Interchange File Format): A standardized file format and directory structure for interchange of JPEG compressed images; includes header parameters (BPS, HEIGHT, HRES), directory tags and offsets.
- Compressed data formats and markers: Defines marker semantics (e.g., DQS - Define quantizer scale selection, DTT - Define tile marker, DTTINDX) and capability indicators to signal decoder requirements.
- Encoder and decoder requirements: Specifies mandatory and optional behaviours for interoperable encoding/decoding of the extension features.
- Compliance testing and examples: Annexes include compliance test definitions, implementation guidance and illustrative examples.
Applications and users
ISO/IEC 10918-3 is intended for organizations and engineers involved in:
- Image codec developers and library maintainers implementing JPEG extensions.
- Digital camera, scanner and imaging device firmware teams requiring advanced tiling or selective refinement.
- Image processing and publishing software that handles large, high‑resolution or multi‑resolution images.
- Archival and interchange systems needing standardized file formats (SPIFF) and compliance guarantees.
- Standards bodies and test labs performing conformance testing or integrating JPEG extensions into profiles.
Related standards
- ISO/IEC 10918‑1 / ITU‑T T.81 - JPEG requirements and guidelines
- ISO/IEC 10918‑2 / ITU‑T T.83 - JPEG compliance testing
- ISO/IEC 10918‑4 - Registration procedures for JPEG Profile, APPn and SPIFF Profile IDs
- Other referenced standards: character sets (ISO/IEC 8859, 10646), colorimetry (CIE), and various ITU‑T/SMPTE recommendations cited in the normative references.
Keywords: ISO/IEC 10918-3, JPEG extensions, SPIFF, variable quantization, selective refinement, tiling, compressed data format, encoder requirements, decoder requirements, compliance testing.
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