Overview
ISO/IEC 21122-2:2022/Amd 1:2022 is an important amendment to the standard titled Information technology - JPEG XS low-latency lightweight image coding system - Part 2: Profiles and buffer models. This amendment introduces a new profile and sublevel specifically designed for 4:2:0 chroma sampling format content, enhancing the existing JPEG XS framework.
JPEG XS is a cutting-edge image coding standard focused on low-latency, lightweight compression with minimal computational overhead, meant to support applications requiring real-time processing and high efficiency. The 2022 Amendment 1 extends the applicability of JPEG XS profiles by including detailed specifications tailored to 4:2:0 chroma subsampled content, which is widely used in broadcasting and streaming video.
Key Topics
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Profiles for 4:2:0 Content
The amendment specifies a new High 420.12 profile, expanding the capabilities of JPEG XS to handle 4:2:0 chroma subsampling natively. This includes characteristics such as bit precision options (8, 10, or 12 bits), smoothing buffer models, and quantizer types.
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Buffer Models and Constraints
Detailed buffer sizing and rate constraints are defined for the new sublevel Sublev4bpp, optimizing performance for 4:2:0 formats. Parameters such as smoothing buffer size in bits, maximum codestream size in bytes, and maximum encoded bitrate (in Mbits/s) ensure efficient decoder buffer management.
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Sublevel Signalling
The amendment introduces signals for sublevels within codestreams, including nominal bits per pixel (bpp) levels such as 12, 9, 6, 4, 3, and 2 bpp. These enable flexible bitrate scalability and adaptation according to system requirements.
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Chroma Sampling Format Support
Profiles now explicitly cover chroma subsampling formats:
- 4:2:0 for the new profile
- 4:0:0, 4:2:2, and 4:4:4 supported in other profiles
This clarifies JPEG XS’s applicability to a variety of imaging systems and content types.
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Profile Identification and Mapping
The amendment updates tables that map profiles to picture header fields and provide binary/hexadecimal values for precise profile identification in codestream headers, supporting interoperability and compliance verification.
Applications
ISO/IEC 21122-2:2022/Amd 1:2022 plays a crucial role in the deployment of JPEG XS compression technology across applications requiring:
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Real-Time Video Streaming
The support for 4:2:0 profiles aligns JPEG XS with common broadcast standards, enabling ultra-low latency, high-fidelity video delivery for live streaming and remote production.
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Professional Media and Broadcasting
Video workflows relying on chroma subsampling for color compression benefit from the defined profiles and buffer models, ensuring compatibility and efficient resource management.
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Video Conferencing and Remote Collaboration
The amendment’s enhancements facilitate lightweight image coding that reduces bandwidth demands without compromising real-time responsiveness critical to communications platforms.
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Embedded and Automotive Systems
Low-latency image coding with defined buffer models supports embedded vision applications, where memory constraints and processing speed are vital.
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Cinematography and Post-Production
The flexibility of supported profiles, including 4:4:4 and Bayer-pattern content, helps maintain image quality in professional editing, grading, and archiving workflows.
Related Standards
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ISO/IEC 21122-1: Describes the core JPEG XS coding system, including syntax and basic coding tools, which this amendment extends.
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ISO/IEC 21122-3: Specifications for transport and container formats for JPEG XS streams.
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ISO/IEC 23008-series: High-efficiency coding standards, which JPEG XS complements by offering low-latency and lightweight options.
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ISO/IEC 11172-series (MPEG-1) and ISO/IEC 13818-series (MPEG-2): Earlier multimedia standards that address different coding needs but underpin the ecosystem in which JPEG XS operates.
Conclusion
ISO/IEC 21122-2:2022/Amd 1:2022 significantly enhances the JPEG XS low-latency lightweight image coding system by introducing comprehensive support for 4:2:0 chroma subsampled content. This amendment provides explicit profiles, buffer models, and signalling mechanisms optimized for low-bitrate, real-time applications common in video streaming, professional media, and embedded imaging. Coupled with the core JPEG XS standards, it delivers a robust framework for efficient, high-quality imaging across diverse industry sectors.
Keywords: JPEG XS, ISO/IEC 21122-2 amendment, 4:2:0 chroma subsampling, low-latency image coding, lightweight image compression, profiles and buffer models, video streaming standard, image coding system, real-time video compression, multimedia standard.