Overview
ISO/IEC 21122-5:2025 - "Information technology - JPEG XS low-latency lightweight image coding system - Part 5: Reference software" provides the official reference software implementation for the JPEG XS standard. This third-edition document delivers a downloadable C-based encoder and decoder that illustrate how to implement the core coding system (Part 1) and profiles/buffer models (Part 2). The package is intended as guidance for implementers and as a validation anchor for conformance testing (see ISO/IEC 21122-4).
Key Topics
- Reference implementation: Sample encoder and reference decoder implementations (C, ISO/IEC 9899:2011 compatible) that decode/produce codestreams conforming to ISO/IEC 21122-1 and optionally ISO/IEC 21122-2.
- Conformance testing support: The reference decoder produces the normative decoding output required for strict conformance comparisons specified in ISO/IEC 21122-4.
- Build and usage guidance: Annex A–C include instructions for building the software, supported image file formats, and usage examples. The software is distributed as a ZIP archive and includes README.md and LICENSE.md.
- Supported image formats: Examples include PGX and NetPBM (PGM/PPM); Annex B documents file layouts and data encodings used by the reference tools.
- Licensing and IP: Licensing terms and contributing parties are documented in the included LICENSE.md; users are advised to review copyright and patent considerations.
- Limitations: The reference software is not a production-grade codec (lacks hardened protection against memory exploits) and does not implement the file-format features of ISO/IEC 21122-3.
Applications
Who uses ISO/IEC 21122-5:2025 and why:
- Codec developers and integrators: Use the sample encoder/decoder as a starting point for production implementations of JPEG XS.
- Conformance test labs and QA teams: Compare outputs of candidate implementations against the reference decoder to validate syntactic correctness and decoding behavior.
- Broadcast, streaming and real-time systems engineers: Evaluate low-latency, lightweight image coding workflows and generate compliant test codestreams.
- Researchers and academic users: Study reference code to understand JPEG XS algorithmic behavior and file-format interactions.
- Tooling vendors: Produce test vectors and tooling for interoperability testing (e.g., difftest_ng conversions to/from PGX).
Related Standards
For implementers and test engineers working with JPEG XS, ISO/IEC 21122-5:2025 is a practical, authoritative resource for reference software, build guidance, supported image formats, and conformance test anchoring.