JPEG XL is a relatively new image compression format, designed to replace older standards such as JPEG and PNG, while offering significant improvements in performance and quality.
The development of JPEG XL was launched in 2017 by the JTC1/SC29/WG1 working group, commonly known as the Joint Photographic Experts Group (JPEG). This group is credited with introducing the original JPEG format in the 1990s, which to this day remains one of the world's most widely used image formats. However, with the evolution of digital needs and the rise of visual content on the Internet, classic JPEG began to show its limits in terms of image quality and compression efficiency.
JPEG XL offers optimized image compression, considerably reducing file size while maintaining high visual quality. This technology enables not only lossy compression, like conventional JPEG, but also lossless compression, offering great flexibility. For example, a JPEG XL image can be 20% lighter than a conventional JPEG file, while maintaining equivalent visual quality.
Despite this progress, adoption of the format remains limited. One of the drawbacks of JPEG XL is its current poor compatibility with browsers and devices, although progress has been made. Google initially integrated JPEG XL support into its Chrome browser, but withdrew it at the end of 2022. Apple, meanwhile, recently supported the format from iOS 17 and macOS Sonoma, paving the way for wider adoption in the future.
A promising format for bandwidth reduction
In a context where the consumption of visual content, especially video, is exploding, reducing file size without compromising quality is essential to improve page loading speed and reduce bandwidth congestion. JPEG XL could be an ideal solution to this problem, particularly where still images are concerned. By reducing file size, it eases network congestion while maintaining superior image quality, which is crucial at a time when global Internet traffic is increasing by 25% a year.
However, the use of this format is still marginal. JPEG XL is currently used more for specific applications, such as the generation of ultra-light artistic images from simple programming scripts. Despite its advantages for lightening the web, major players like Google prefer alternatives such as WebP or the recent Jpegli. Apart from a few Apple products, few devices and services currently support this format, limiting its short-term potential. This lack of compatibility hinders its integration into image production workflows, whether for photographers, designers or web developers.
Advanced technical features for photography and animation
JPEG XL offers a number of interesting technical features, including a wide color gamut and extended dynamic range (HDR), making this format particularly well-suited to photography and the creation of high-quality images. It also supports the encoding of synthetic images and animations, offering great versatility. What's more, its ability to re-encode lossless JPEG files and reduce their size by 20% is a considerable advantage for users wishing to preserve the integrity of their files while optimizing their storage.
Limited uses despite royalty-free format
One of the major advantages of JPEG XL is that it is a royalty-free format, which means it can be used without license fees, unlike other compression formats such as HEIF, which is used on Apple devices to save photos. This feature should, in theory, encourage its adoption by a wide range of applications, notably on the web and in mobile applications.
JPEG XL features
JPEG XL works by combining advanced compression techniques to reduce file size while maintaining high image quality. It allows both lossy compression, like conventional JPEG, and lossless compression, making it more flexible for a variety of uses. Here are the key stages and principles of its operation:
- Lossy and lossless compression
With loss this reduces file size by eliminating certain visual data, but in such a way that the loss of quality is minimal or imperceptible to the human eye.
Lossless compresses images without deleting any information, enabling exact reconstruction of the original image after decompression. - Progressive encoding : JPEG XL uses progressive encoding, which allows a low-resolution version of an image to be loaded first, then refined as more data is downloaded. This speeds up image loading on the web, improving the user experience, especially for slower connections.
- Discrete cosine transform (DCT) and modified wavelets : To compress images, JPEG XL uses Discrete Cosine Transform (DCT), an algorithm that divides an image into several blocks and analyzes light frequencies. For more complex details, it uses modified Haar wavelets, a technique that preserves fine image detail while limiting visual artifacts.
- Color and HDR : JPEG XL manages a wide color gamut and supports high dynamic range (HDR) images. This enables it to render images with richer contrast and color, which is particularly important for professional photography and high-quality images.
- Alpha channel encoding and animation : The format also supports alpha channel encoding, making it possible to manage transparency in images, an essential feature for graphic designers. What's more, JPEG XL is capable of compressing animations, making it more versatile and suitable for different types of visual media.
- Low-power decoding : Unlike other formats that sometimes require specialized chips for decoding, JPEG XL is designed to run efficiently on a wide range of devices, without requiring much processing power or energy, making it compatible with mobile and low-power devices.
- Compatibility and transcoding : JPEG XL includes a transcoding mode for conventional JPEG images, enabling existing files to be converted to JPEG XL without loss of quality. This facilitates its gradual adoption, as users can continue to use their existing JPEG files while benefiting from improved compression.
In the years to come, it will be interesting to see whether JPEG XL manages to stand out sufficiently to establish itself as a standard for still images, or whether it will remain a niche format used by creators and technophiles. One of the key factors will undoubtedly be its adoption by browsers and major platforms, as well as developers' interest in integrating this format into their tools.
