JPEG XL Image
| Format | JPEG XL Image |
|---|---|
| Short name | JPEG XL |
| Category | media |
| Platforms | Windows, macOS, Linux, iOS, Android, QNX |
| Crush support | Supported (ImageParser) |
| Status | Reviewed |
| Last reviewed | 2026-10-04 |
Forensic relevance
Next-generation image format standardised as ISO/IEC 18181 (2022). Supports both lossy and lossless compression with significantly better efficiency than JPEG; lossless JPEG transcoding (bit-exact round-trip) is a first-class feature. Two container variants exist with distinct magic sequences: the bare codestream (\xff\x0a at offset 0) and the ISOBMFF/JXL container (12-byte signature starting with \x00\x00\x00\x0c\x4a\x58\x4c at offset 0), which supports EXIF, XMP, and multiple frames. Adoption is growing in high-end cameras, Apple ecosystem (iOS 17+, macOS Sonoma+), and some Android OEMs. iPhone ProRAW (iOS 18+) can store DNG files with JPEG XL-compressed image data (DNG 1.7) — these keep the .dng extension. Forensically relevant: timestamp and GPS metadata in EXIF boxes, lossless re-encoding makes tampering detection harder than with JPEG, and the format's novelty means older tools may fail to parse it. A C2PA (Content Credentials) manifest, when present in the box-form container, is a top-level JUMBF superbox — the bare codestream variant cannot carry one at all. Can record generating/editing software and an IPTC Digital Source Type — a direct AI-generation/-editing signal.
Signatures
| Offset | Hex | ASCII (non-printable as .) | Description |
|---|---|---|---|
| offset 0 (0x0) | FF 0A | .. | JPEG XL naked codestream signature |
| offset 0 (0x0) | 00 00 00 0C 4A 58 4C 20 0D 0A 87 0A | ....JXL .... | JPEG XL ISOBMFF/JXL container signature |
Known extensions
.jxl
References
- JPEG XL — official specification overview https://jpeg.org/jpegxl/
- ISO/IEC 18181-1:2024 — JPEG XL core coding system https://www.iso.org/standard/85066.html
- JPEG XL format overview (libjxl docs) https://github.com/libjxl/libjxl/blob/main/doc/format_overview.md
- JPEG XL file format overview (Library of Congress) https://www.loc.gov/preservation/digital/formats/fdd/fdd000538.shtml
- Supporting JPEG XL compression in Apple ProRAW capture https://juniperphoton.substack.com/p/supporting-jpeg-xl-compression-in
- C2PA Technical Specification (Content Credentials) https://spec.c2pa.org/specifications/specifications/2.4/specs/C2PA_Specification.html
Cite this entry
Crush Format Reference, “JPEG XL Image”. https://kalink0.github.io/crush-forensics/formats/jpeg-xl/ — source: crush/data/build_formats_db.py at commit 640a2a9928f4e36a976b89901512a8dce824d093, built 2026-10-21 06:46:19 UTC.
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