JPEG XS

Key takeaways

JPEG XS belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect JPEG XS to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of JPEG XS from memory before moving on to harder problems.

Reference excerpt

JPEG XS (standardized as ISO/IEC 21122) is an image and video codec that offers both visually and mathematically lossless quality. It is a special-purpose codec that is specifically designed to allow for low-complexity and low-latency implementations. Target applications of the standard include streaming high-quality content for professional video over IP (SMPTE ST 2022 and ST 2110) in broadcast and other applications, virtual reality, drones, autonomous vehicles using cameras, gaming. Although there is not an official acronym definition, XS was chosen to highlight the extra small and extra speed characteristics of the codec.

Features Three main features are key to JPEG XS:

Visually transparent compression: XS compressed content is indistinguishable from the original uncompressed content (passing ISO/IEC 29170-2 tests, also called AIC-2) for compression ratios between 2:1 and 10:1. Low latency: The total end-to-end latency, introduced by the JPEG XS compression-decompression cycle, is minimal. Depending on the configuration, XS typically imposes only between 1 and 32 lines of additional end-to-end latency, when compared to the same system using uncompressed video. Lightweight: JPEG XS is designed to have low computational and memory complexity, allowing for efficient low-power and low-resource implementations on various platforms such as CPU, GPU, FPGA and ASIC. Relying on these key features, JPEG XS is suitable for any application where uncompressed content is the norm, yet still allowing for significant savings in the required bandwidth usage, preserving quality and low latency. Among the targeted use cases are video transport over professional video links (like SDI and professional video over IP), real-time video storage, memory buffers, omnidirectional video capture and rendering, and image sensor compression (for example in cameras and in the automotive industry). JPEG XS favors visually lossless quality in combination with low latency and low complexity, over data reduction through compression. It is not a direct competitor to alternative image codecs like JPEG 2000 and JPEG XL or video codecs like AV1, AVC/H.264 and HEVC/H.265 which tend to focus on compression efficiency. Other important features are:

Exact bitrate allocation: JPEG XS allows an accurately targeted bitrate to perfectly match the available bandwidth (also referred to as constant bitrate). Multi-generation robustness: JPEG XS allows for at least 10 encoding-decoding cycles, without significant quality degradation. This feature allows for example transparently chaining of multiple devices that recompress the signal, without any significant quality degradation taking place. Multi-platform interoperability: The algorithms used in JPEG XS allow for efficient implementations on different platforms, like CPU, GPU, FPGA and ASIC. Each of these platform architectures is best exploited when a specific degree of parallelism is available in the implementation. For instance, a multi-core CPU implementation will leverage a coarse-grained parallelism, while GPU or FPGA will work better with a fine-grained parallelism. Moreover, the choice of parallelism used in the implementation at the encoder will not affect that of the decoder. This means that real-time encoding and decoding between platforms is possible, without sacrificing the low-complexity, low-latency or high-quality properties. Support for mathematical lossless coding (MLS): JPEG XS is also capable of coding images in a mathematically lossless way, to achieve perfect reconstruction at the decoder side (new profile supported by 2nd edition). Support for High Dynamic Range (HDR) content: The current version of JPEG XS supports bit-depths of up to 16 bits per component, and it provides several parameterizable non-linear transforms to efficiently compress HDR content. Support for RAW Bayer/CFA compression: JPEG XS has also the capability to compress color filter array (CFA) content, such as RAW Bayer content produced by digital cameras. A special color transform, called Star-Tetrix, allows for efficient and direct compression of the original RAW sample values, without the need for converting the Bayer samples to RGB samples first. Accurate flow control: A JPEG XS encoder continuously monitors the amount of bits sent out, and adjusts its rate allocation process to neither overflow nor underflow a normatively defined decoder input buffer.

Application domains JPEG XS is actively used in several application domains.

Transport over video links and IP networks Video bandwidth requirements are growing as video resolutions, frame rates, bit depths, and the number of video streams are constantly increasing. Although the capacities of video links and communication channels are also growing, there are applications where the reduced data rate afforded by JPEG-XS is advantageous. Both the broadcast and pro-AV markets are shifting towards AV-over-IP-based infrastructure, with a preference going to Gigabit Ethernet links for remote production and faster fiber-based Ethernet for in-house facilities. Given the available bandwidth and infrastructure cost, relying on uncompressed video may be cost-prohibitive if 4K, 8K, increased bit depths for HDR, and higher framerates need to be supported. With XS, it is for example possible to repurpose existing SDI cables to transport 4K60 over a single 3G-SDI (at 4:1 compression ratio), and even over a single HD-SDI (at 8:1 compression ratio). Similar scenarios can be used to transport 8K60 content over various SDI cable types (e.g. 6G-SDI and 12G-SDI). Alternatively, XS enables transporting 4K60 content over Gigabit Ethernet and 8K60 over 5G or 10 Gigabit Ethernet, which would be impossible without compression. The following table shows expected compression ranges for some typical use cases.

Real-time video storage and playout Related to the transport of video streams is the storage and retrieval of high-resolution streams where bandwidth limitations similarly apply. For instance, video cameras use internal storage like SSD drives or SD cards to record high-resolution streams of images, yet the maximum data rates of such storage devices may be below that required to store uncompressed video in real time.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with JPEG XS

Start with the simplest possible case. Write down what JPEG XS claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to JPEG XS before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about JPEG XS ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of JPEG XS

In research: JPEG XS appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses JPEG XS in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: JPEG XS is common in secondary-school and first-year university syllabi. It links to neighbouring topics IEC standards, ISO standards, Image compression, so understanding it makes those chapters shorter.
In everyday life: Look for JPEG XS outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study JPEG XS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what JPEG XS means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain JPEG XS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is JPEG XS in simple terms?

JPEG XS (standardized as ISO/IEC 21122) is an image and video codec that offers both visually and mathematically lossless quality. It is a special-purpose codec that is specifically designed to allow for low-complexity and low-latency implementations.

Why does JPEG XS matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study JPEG XS?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on JPEG XS.