ISO/IEC 18477-2:2016 PDF

Overview

ISO/IEC 18477-2:2016 defines JPEG XT Part 2 - a codestream and coding format for high dynamic range (HDR) continuous‑tone still images. Designed as a scalable extension of legacy JPEG, it enables storage and interchange of HDR and wide‑gamut photographic content while remaining backward compatible with Rec. ITU‑T T.81 | ISO/IEC 10918‑1 (baseline JPEG). JPEG XT provides a migration path so existing JPEG toolchains can decode a low‑dynamic‑range, 8‑bit version of images encoded with this standard.

Key technical topics and requirements

• Scalable compression and codestream structure: Specifies a codestream composition that carries both legacy-compatible LDR data and HDR residual data (residual codestream).
• HDR coding and reconstruction: Supports multiple‑component images in floating‑point (optimized for 32‑bit float HDR and wide colour gamut).
• Backward compatibility: Legacy decoders reconstruct an 8‑bit per component, lower-quality image; full HDR requires a JPEG XT‑aware decoder.
• Decoder and encoder requirements: Defines high‑level functional blocks for decoding (e.g., inverse decorrelation, base mapping, residual decode, HDR reconstruction) and sets conformance language and operator conventions.
• Codestream syntax: Details Main Profile header structure, parameter ASCII and binary segments, and residual codestream segment layout.
• Terminology and normative rules: Includes terms/definitions, symbols, mathematical operator rules, and checksum computation (Annex A).
• References and colour management: Normative references include ISO/IEC 10918‑1, ISO/IEC 18477‑1 (core system), and IEC 61966‑2‑1 (sRGB).

Practical applications

• Archival and digital photography workflows that require preservation of HDR and wide‑gamut imagery.
• Imaging software, photo editors, and transcoding tools that need to produce files compatible with legacy JPEG decoders while offering HDR fidelity to capable clients.
• Camera firmware and capture pipelines that output compact, interoperable HDR imagery.
• Printing, broadcast, and visual effects pipelines where high precision colour and luminance are required.

Who should use this standard

• Codec implementers and multimedia software developers building JPEG XT encoders/decoders.
• Digital asset managers and archivists planning long‑term storage of HDR photographic content.
• Camera and imaging device manufacturers seeking an interoperable HDR file format.
• Standards and QA teams verifying conformance, compatibility, and migration strategies from legacy JPEG.

Related standards

• ISO/IEC 18477‑1 - Core coding system (JPEG XT framework)
• ISO/IEC 10918‑1 (Rec. ITU‑T T.81) - Legacy JPEG baseline
• IEC 61966‑2‑1 - sRGB colour space

Keywords: ISO/IEC 18477‑2, JPEG XT, HDR images, scalable compression, backward compatible JPEG, residual codestream, wide colour gamut.