(registered 2024-03-04, last updated 2024-03-04)

Media type name: image

Media subtype name: jxl

Required parameters: N/A.

Optional parameters: N/A.

Encoding considerations: binary

Files are binary and should be transmitted in a suitable encoding without CR/LF conversion, 7-bit stripping etc.; base64 is a suitable encoding.

Security considerations: The conveyed coded image files defined in ISO/IEC 18181-2 use a structure that can store image data, metadata corresponding to this image data, and other user-defined data. The data files have an extensible structure, so that it is theoretically possible that metadata fields are defined in the future that can be used to induce particular actions on the part of the recipient, thus presenting additional security risks, but this type of capability is currently not supported in the current referenced specifications.

Image dimensions can be large, and image files can contain multiple frames as well as many components. A small compressed file could decode to a large uncompressed object, which can lead to out of memory failure conditions. Additionally, it can potentially take significant computational effort to decode even an image file that has a small compressed or uncompressed size, potentially leading to denial-of-service issues. However, it should be possible to implement a conforming decoder that has bounded memory usage and that runs in a bounded amount of time for a given image size, so this is a matter of quality of implementation rather than an inherent security risk.

Interoperability considerations: JPEG XL image files can conform to a profile and level of capabilities (as specified in ISO/IEC 18181-1, Annex M) – not all of which may be supported by a receiving decoder. As a result, implementations may attempt to decode and display an encoded JPEG XL image only to determine that the image cannot be rendered, either partially or in full.

JPEG image files (ISO/IEC 10918-1:1994) can be losslessly recompressed to JPEG XL images (with improved compression), and the original JPEG file can be reconstructed using the JPEG Bitstream Reconstruction Data as described in ISO/IEC 18181-2.

Published specification: ISO/IEC 18181-2, Information technology – JPEG XL image coding system – Part 2: File format

Applications which use this media: Multimedia, Imaging, Pictures, Scientific

Fragment identifier considerations: None

Restrictions on usage: None

Additional information:

1. Deprecated alias names for this type: N/A.
2. Magic number(s): Starts with either the 2-byte sequence 0xFF 0A (a direct JPEG XL codestream without box structure) or the 12-byte sequence 0x0000 000C 4A58 4C20 0D0A 870A (an ISOBMFF box structure starting with the JPEG XL
Signature box), as specified in ISO/IEC 18181-2.
3. File extension(s): jxl
4. Macintosh file type code: N/A.
5. Object Identifiers: N/A.

General Comments: It should be noted that selected metadata fields may encompass information partly intended to protect the image against unauthorized use or distribution. In this case, the intention may be that alteration or removal of the data in the fields would be treated as an offence. Metadata fields may also contain information about the source of the image content.

Person to contact for further information:

1. Name: ISO/IEC JTC 1/SC 29/WG 1 Convenor
2. Email: sc29-sec&itscj.ipsj.or.jp

Intended usage: COMMON

Author/Change controller: ISO/IEC JTC 1