Overview
ISO/IEC 18477-5:2018 - Part 5 of the ISO/IEC 18477 series (commonly known as JPEG XT) - specifies reference software for scalable compression and coding of continuous‑tone still images. The standard provides source code and executable reference implementations (decoder and sample encoder) that demonstrate features across multiple ISO/IEC 18477 parts, primarily targeted at photographic content and high dynamic range (HDR) workflows. Reference materials, build instructions and usage guidance are supplied (see Annexes A–D) and were compiled and tested on Linux and Windows at the time of publication.
Key topics and technical requirements
- Reference implementations: Provides decoder and sample encoder software for ISO/IEC 18477 parts including -1, -3, -6, -7, -8, -9 (codestreams, box file format, IDR integer coding, HDR floating‑point, lossless/near‑lossless, alpha channel).
- Supported coding modes: Implements baseline, extended sequential and progressive Huffman coding modes and common extensions such as JFIF (ITU‑T T.871 | ISO/IEC 10918‑5).
- Formats and terminology: Defines and uses image container/formats referenced in the series (PPM, PFM, PNM) and codestream concepts for conformance testing.
- Purpose and limitations:
- Intended as a guideline for implementers and a basis for conformance testing (conformance procedures are detailed in ISO/IEC 18477‑4).
- Reference software does not replace normative requirements - it illustrates behaviour but does not guarantee encoding quality or performance characteristics.
- ISO/IEC 18477‑1 does not include certain modes from legacy JPEG (e.g., arithmetic/hierarchical/lossless modes from Rec. ITU‑T T.81).
- Distribution: Source archives (e.g., reference1367abcd89.zip and reference7b.zip) and unpack/compile instructions are provided via the ISO standards site.
Practical applications and who should use it
- Codec developers: Use the reference decoder/encoder as a starting point for implementing JPEG XT‑compliant software.
- Quality assurance and interoperability teams: Generate test codestreams and run non‑exhaustive conformance checks against ISO/IEC 18477 constraints.
- Imaging software vendors & camera manufacturers: Evaluate HDR/IDR workflows, alpha channel coding and scalable compression options for photographic pipelines.
- Researchers and educators: Study practical implementations of scalable image coding and HDR floating‑point coding techniques.
- Archivists and workflow integrators: Evaluate backward compatibility with legacy JPEG while supporting extended dynamic range and lossless options.
Related standards
For access to the reference software and full normative text, see the ISO page for ISO/IEC 18477-5:2018 (standards.iso.org/iso-iec/18477/-5/ed-1/en).
Open preview (PDF)Information technology — Scalable compression and coding of continuous-tone still images — Part 5: Reference software
