Microsoft Windows JPEG XL Image Extension v1.0
JPEG XL is a next-generation image format designed to offer significant improvements over existing formats like JPG, PNG and GIF. JPEG XL is the successor to JPG/JPEG with its advantage of small file size, but also has the advantages of PNG and GIF: transparency and animation. JPEG XL has this file extension: *.jxl
JPEG XL: A Comprehensive Overview
JPEG XL is a next-generation image format designed to address the limitations of older formats like JPEG while introducing advanced features for modern imaging needs. Standardized as ISO/IEC 18181, it is developed by the Joint Photographic Experts Group (JPEG) in collaboration with the International Electrotechnical Commission (IEC) and the International Organization for Standardization (ISO). This format is tailored for high-quality image compression, efficient web delivery, and professional workflows, making it a versatile and future-proof solution for digital imaging.
Historical Context and Development
JPEG XL was conceived to succeed the widely used JPEG format, which has been a cornerstone of digital imaging since its introduction in 1992. While JPEG revolutionized image sharing and storage, its limitations—such as visible compression artifacts at lower bitrates, lack of support for modern features like high dynamic range (HDR), and inefficiencies in lossless compression—became apparent over time.
The “XL” in JPEG XL stands for “long-term,” reflecting its goal of being a sustainable format that can adapt to future imaging technologies. The development team includes notable contributors such as Jon Sneyers, Jyrki Alakuijala, and Luca Versari, who have integrated ideas from Google’s PIK format and Cloudinary’s FUIF format into JPEG XL’s architecture.
Key Features of JPEG XL
JPEG XL introduces a host of features that set it apart from legacy formats like JPEG and even newer competitors like HEIC and WebP. These features cater to diverse use cases, from web delivery to professional photography.
1. Compression Efficiency
Lossy and Lossless Compression: JPEG XL supports both lossy and lossless compression modes. Lossless compression achieves smaller file sizes than PNG (up to 35% smaller) while maintaining pixel-perfect fidelity.
High Compression Ratios: In lossy mode, JPEG XL achieves up to 60% smaller file sizes compared to legacy JPEG without visible artifacts. It offers graceful quality degradation across a wide range of bitrates.
Reversible Transcoding: Existing JPEG files can be losslessly transcoded into JPEG XL, reducing their size by approximately 20%. These files can be converted back to their original JPEG form without any loss of data.
2. Wide Color Gamut and HDR Support
JPEG XL is optimized for modern display technologies capable of reproducing rich colors and high dynamic range. It supports wide color gamuts like Rec. 2100 with PQ or HLG transfer functions, ensuring compatibility with HDR content.
3. Advanced Image Features
Layer Support: The format allows multiple layers within a single file, which is useful for editing workflows and storing additional data like selection masks or spot colors.
Alpha Channels: Transparency is supported through alpha channels, enabling compositing and blending.
Animation: JPEG XL supports animated images with multiple frames that can have variable durations or serve as editing layers.
Ultra-High Resolution: The format can handle images up to 1 terapixel in size, making it suitable for applications requiring extremely high resolutions1.
4. Efficient Encoding and Decoding
JPEG XL is designed to be computationally efficient:
It can encode and decode images as quickly as legacy JPEG using libjpeg-turbo.
It is an order of magnitude faster than HEIC with x265 encoding.
The format does not require specialized hardware acceleration, making it accessible on a wide range of devices.
5. Web Optimization
JPEG XL includes several features tailored for web environments:
Progressive Rendering: Sophisticated progressive decoding allows images to load incrementally, improving user experience on slow networks.
Minimal Header Overhead: The format ensures that metadata does not bloat file sizes.
Responsive Design: Images render well across various devices with different screen sizes and resolutions.
6. Future-Proof Design
JPEG XL has no baked-in limitations regarding image dimensions or color precision, ensuring compatibility with future imaging technologies. It can store unconventional data types like depth maps or thermal imaging data and includes mechanisms for gradual feature extension2.
Technical Details
JPEG XL employs two primary encoding modes:
VarDCT Mode
This mode uses variable-block-size Discrete Cosine Transform (DCT), an evolution of the traditional DCT used in legacy JPEG. Blocks can vary in size from 2×2 to 256×256 pixels and may take non-square shapes (e.g., 16×8). This flexibility allows better adaptation to image content, improving compression efficiency while maintaining high fidelity1.
Modular Mode
The modular mode handles lossless content encoding and near-lossless compression. It also manages auxiliary data like adaptive quantization weights and filter strengths. This mode is particularly useful for synthetic imagery or images requiring precise editing workflows1.
Applications of JPEG XL
JPEG XL’s versatility makes it suitable for a wide range of applications:
Web Delivery
The format’s efficient compression and progressive rendering make it ideal for web environments where speed and bandwidth are critical.
Professional Photography
With support for wide color gamuts, HDR content, and up to 32-bit sample precision, JPEG XL caters to professional photographers who demand high-quality outputs.
Digital Printing
The inclusion of CMYK support and spot colors ensures that JPEG XL meets the requirements of digital printing workflows.
Cloud Storage
Its ability to store large amounts of image data efficiently makes it valuable for cloud storage solutions.
Comparison with Other Formats
| Feature | JPEG | PNG | WebP | HEIC | JPEG XL |
|---|---|---|---|---|---|
| Lossless Compression | No | Yes | Yes | Yes | Yes |
| Lossy Compression | Yes | No | Yes | Yes | Yes |
| Transparency Support | Limited | Yes | Yes | Limited | Yes |
| Wide Color Gamut | No | Limited | Limited | Yes | Yes |
| HDR Support | No | No | No | Yes | Yes |
| Animation | No | No | Yes | Limited | Yes |
| File Size Efficiency | Moderate | Large | High | High | Very High |
| Encoding Speed | Fast | Slow | Moderate | Slow | Fast |
Adoption and Software Support
Since its standardization in 2022, JPEG XL has gained traction but still faces limited adoption compared to older formats. However, support is growing across operating systems, web browsers, and image-related software:
Operating Systems: Windows Imaging Component now supports thumbnail previews for JPEG XL files.
Browsers: Chrome versions M91-M109 supported the format behind a feature flag.
Image Editors: Tools like Paint.NET, XnView, IrfanView, and ImageGlass have added support for JPEG XL
Challenges
Despite its advantages, JPEG XL faces some challenges:
Limited Awareness: Many users remain unaware of the format due to the dominance of older standards like JPEG.
Software Ecosystem: While growing, software support is not yet universal.
Competition: Formats like HEIC (used by Apple) pose significant competition due to their integration into popular ecosystems.
Conclusion
JPEG XL represents a significant leap forward in image compression technology. Its combination of lossy and lossless compression modes, support for modern imaging requirements like HDR and wide color gamut, and efficient encoding make it a strong contender for replacing legacy formats. While adoption may take time due to entrenched alternatives like JPEG and HEIC, its open standard nature ensures that it remains accessible to developers and users alike.
As display technologies evolve and demand for high-quality visuals grows across industries—from photography to web design—JPEG XL is well-positioned to become a cornerstone in the future of digital imaging.
