Overview
ISO/IEC 21122-1:2024 - "Information technology - JPEG XS low‑latency lightweight image coding system - Part 1: Core coding system" defines the core codestream syntax and decompression (decoder) process for JPEG XS. The standard targets continuous‑tone gray‑scale and colour images and specifies a lightweight, low‑latency image coding system capable of visually lossless and lossless operation at typical compression ratios of about 2:1 to 18:1 (and higher depending on image content). It enables encoder and decoder implementations that limit end‑to‑end latency to a fraction of the frame size; transmission buffer modeling is out of scope.
Key topics and technical requirements
- Codestream syntax: formal definition of the compressed image representation required to reconstruct image samples.
- Decoding processes: normative procedures for converting compressed codestreams into reconstructed images.
- Encoder guidance: recommended processes and constraints for producing compliant codestreams.
- Wavelet processing: wavelet decomposition and inverse transforms used in core coding (see discrete wavelet transform annex).
- Quantization and inverse quantization: quantizer definitions including deadzone quantizers and guidance for magnitude/sign handling.
- Entropy decoding: bitplane, code group and packet structures, plus entropy decoding mechanisms.
- Multi‑component transforms: reversible and non‑reversible component transformations (e.g., RCT and CFA‑aware transforms).
- Low‑latency constraints: lightweight toolset and frame/precinct/slice structures that support limited buffering and fractional‑frame latency.
- Lossless support & screen content tools: third edition adds lossless coding up to 16 bits per sample and improved tools for screen content image compression.
- Normative annexes: codestream syntax, image data structures, entropy decoding, quantization, DWT, component transforms, frame buffer and more.
Practical applications
- Real‑time contribution and production workflows (live broadcast, remote production) where low latency and visually lossless quality are required.
- Professional video and studio infrastructure for frame‑accurate, high‑quality transmission between devices.
- Sensor and embedded camera links where efficient, low‑complexity decoders are needed.
- AR/VR and low‑latency streaming where end‑to‑end delay must be minimized.
- Screen content and graphics transmission using the added screen‑content coding tools.
Who should use this standard
- Codec implementers and firmware/hardware designers (encoders/decoders)
- Broadcast and video system architects
- Camera and imaging device manufacturers
- Software developers for real‑time streaming and media processing
- Standards and compliance teams evaluating low‑latency image transport
Related standards
- This document is Part 1 (core) of the ISO/IEC 21122 (JPEG XS) series. Refer to ISO and IEC websites for other parts in the series (profiles, transport, application guidelines) and for patent/licensing information.
Keywords: ISO/IEC 21122-1:2024, JPEG XS, low-latency image coding, codestream syntax, discrete wavelet transform, entropy decoding, quantization, lossless coding, screen content, real-time video.