ISO/IEC 18477-8:2020 - JPEG XT Lossless and Near-Lossless Coding
Overview
ISO/IEC 18477-8:2020 specifies extensions to the JPEG XT family to enable lossless and near-lossless coding of continuous-tone still images while remaining backwards compatible with the core JPEG XT system (ISO/IEC 18477-1). Often called JPEG XT, this part defines a scalable codestream format optimized for photographic content across 8‑ to 16‑bit integer samples and 16‑bit floating‑point samples. Legacy JPEG decoders conforming to ITU‑T T.81 / ISO/IEC 10918‑1 can still reconstruct an 8‑bit LDR version from compliant codestreams.
Key Topics
- Scalable compression: supports progressive and layered coding from lossy LDR to full-range lossless representations.
- Lossless & near-lossless modes: extensions that enable exact or bounded-loss reconstruction for intermediate and HDR image data.
- Compatibility with legacy JPEG: codestream structured so traditional JPEG toolchains can decode a base 8‑bit image.
- Supported sample types: integer samples (8–16 bits) and 16‑bit floating point samples for HDR workflows.
- Box-based file format integration: uses the box file format defined in ISO/IEC 18477-3 for metadata and stream organization.
- Normative processing elements: includes procedures for entropy coding, DCT (including fixed‑point DCT), component decorrelation, upsampling, quantization and noise shaping (see Annexes A–H).
- Profiles and conformance: encoder/decoder requirements and profiles define interoperable subsets and conformance rules.
Applications
ISO/IEC 18477-8:2020 is valuable where high image fidelity and interoperability are required:
- Professional digital photography and raw workflows - preserve full dynamic range and precision while enabling legacy preview compatibility.
- Digital archiving and preservation - lossless storage of high‑bit‑depth images with standardized decoding.
- Imaging software and codecs - implementers building encoders/decoders or image-processing libraries that need scalable lossy-to-lossless pipelines.
- Publishing, printing and color management - ensure high-precision originals are stored and transported without loss.
- Broadcast and HDR content delivery - store and transmit HDR still images with backward-compatible access for LDR devices.
Who uses it: codec developers, camera manufacturers, image-editing and DAM software vendors, archivists and standards engineers.
Related Standards
Keywords: ISO/IEC 18477-8:2020, JPEG XT, lossless coding, near-lossless, scalable compression, HDR imaging, 16-bit floating point, backward compatible JPEG.
Open preview (PDF)Information technology — Scalable compression and coding of continuous-tone still images — Part 8: Lossless and near-lossless coding
