What Is JPEG XL and Why Does It Replace JPEG?

JPEG XL (JXL) is an open, royalty-free raster image format designed by the Joint Photographic Experts Group (JPEG) to serve as a universal standard across digital media. Developed as a successor to both the legacy JPEG standard from 1992 and contemporary alternatives like WebP and AVIF, JPEG XL delivers substantially higher compression efficiency, broad feature parity with modern display requirements, and unique backwards-compatibility features. This article outlines the architectural advantages of JPEG XL and examines why it was engineered to outperform both historical and competing modern image formats.

What Is JPEG XL?

Standardized under ISO/IEC 18181, JPEG XL is a still-image format created by merging Google’s PIK architecture and Cloudinary’s Free Universal Image Format (FUIF). Designed from the ground up specifically for still photography and digital graphics, it provides both lossy and lossless compression. Unlike video-derived image formats, its encoding engines—primarily VarDCT (Variable-block Discrete Cosine Transform) for photographic content and Modular for synthetic graphics and lossless data—are tailored exclusively for the requirements of high-performance static rendering.

Why JPEG XL Was Designed to Replace Legacy JPEG

The original JPEG format has served as the web's default visual standard for over three decades, but its aging technical foundation creates significant bottlenecks on modern displays and networks:

• Lossless Transcoding of Existing JPEGs: JPEG XL can losslessly convert legacy JPEG files into the JXL format, immediately reducing file sizes by approximately 16% to 22% without any loss of visual quality. The original JPEG bitstream can be reconstructed bit-for-bit from the JXL file at any time, allowing web hosts and archives to save storage space without permanently discarding their original assets.
• Massive File Size Reductions: When compressing raw images directly, JPEG XL achieves approximately 60% smaller file sizes than legacy JPEG at visually indistinguishable quality levels.
• Support for Modern Display Technologies: Legacy JPEG is fundamentally limited to 8-bit color depth and the standard sRGB color space. JPEG XL natively supports High Dynamic Range (HDR), wide color gamuts (such as Rec. 2020 and Display P3), up to 32-bit floating-point color depth per channel, and alpha channel transparency.
• Superior Progressive Decoding: While traditional JPEG supports a basic progressive scan, JPEG XL features responsive, multi-resolution progressive decoding. Clients receive a recognizable preview using a fraction of the total byte count, followed by sharp details as data streams in, optimizing web performance on slow connections.

Why JPEG XL Competes with Modern Formats (AVIF and WebP)

In recent years, formats derived from video codecs—such as WebP (derived from VP8) and AVIF (derived from AV1)—emerged to replace JPEG. While they offer improvements over legacy standards, they introduce trade-offs that JPEG XL was explicitly engineered to eliminate:

• Dedicated Still-Image Architecture: Video codecs are optimized for moving frames where individual compression artifacts are masked by temporal motion. When applied to high-resolution still photography, video-derived formats like AVIF can cause unwanted blurriness, washed-out fine textures, or shift colors in subtle gradients. JPEG XL uses psychovisual modeling specifically tuned for high-resolution static viewing.
• Encoding and Decoding Speed: AVIF requires substantial computational power to encode, which causes latency on high-volume servers and consumes battery on mobile devices. JPEG XL encodes significantly faster than AVIF while maintaining comparable or superior visual quality, making real-time encoding feasible for production web pipelines and digital cameras.
• Massive Image Dimensions: Formats based on video profiles impose hard limits on frame sizes without complex tiling schemes (for example, basic AV1 limits frames to 4K or 8K resolution). JPEG XL can handle images exceeding 1 billion pixels on each side, along with arbitrary aspect ratios, making it suitable for scientific imaging, professional print, and panoramic photography.
• Rich Metadata and Auxiliary Channels: JPEG XL supports complex compositing needs, including animations, depth maps, thermal data, and layered images within a single container, bypassing the container limits of older and competing formats.

The Path to a Universal Format

JPEG XL eliminates the fragmentation of using different formats for different needs—such as PNG for transparency, legacy JPEG for photos, and GIF or WebP for simple animations. By delivering state-of-the-art compression, lossless reversibility for legacy files, and support for high-end color standards, JPEG XL was engineered to serve as a complete, single replacement for the entire ecosystem of digital visual media.