HEJ2K

JPEG 2000 Image (HEIF Container)

image/hej2k Released 2019 · by ISO/IEC JTC 1 / ITU-T

HEJ2K (High Efficiency JPEG 2000) is a format that stores still images encoded with the JPEG 2000 codec (including HTJ2K) inside a High Efficiency Image File Format (HEIF) container. It combines the powerful wavelet-based compression of JPEG 2000 with the flexible, metadata-rich architecture of the ISOBMFF standard.

Professional & Archival Transparency Progressive ✦ HDR Production Ready

Technical Specifications

MIME Type

image/hej2k

Extensions

.hej2

Container

HEIF / ISOBMFF (ISO/IEC 15444-16)

Compression

Lossy & Lossless

Algorithms

JPEG 2000HTJ2K

Color Depth

8-bit, 10-bit, 12-bit, 16-bit

Metadata

EXIF XMP ICC

Capabilities

Transparency

Animation

Progressive Loading

Alpha Channel

HDR Support

Official Specification

Aliases: image/heif

Magic Bytes & HTTP Headers

File Signature (Magic Bytes)

XX XX XX XX 66 74 79 70 6A 32 6B 69

ASCII: ....ftypj2ki

HTTP Headers

Content-Type: image/hej2k

HTML Accept Attribute

accept="image/hej2k, .hej2"

Browser Support Matrix

Browser	Status	Min Version
Chrome	Not Supported	—
Firefox	Not Supported	—
Safari	Not Supported	—
Edge	Not Supported	—
Internet Explorer	Not Supported	Legacy

Advantages & Limitations

Advantages

Brings the extensive capabilities of the HEIF container (like EXIF/XMP, thumbnails, and depth maps) to JPEG 2000
Supports mathematically lossless compression via wavelet transformation
High scalability and progressive decoding out of the box

Limitations

Extremely limited software support outside of niche industries
Zero native compatibility with web browsers
High computational complexity compared to simpler formats like JPEG or PNG

Developer Code Snippets

import magic
print(magic.from_file('image.hej2', mime=True)) # May output generic 'image/heif' based on system libraries

const FileType = require('file-type');
const type = await FileType.fromFile('image.hej2');
console.log(type?.mime); // Standard libraries may fall back to image/heif without specific j2ki definitions

import "net/http"
// Custom ISOBMFF parsing is required to read the 'j2ki' brand inside the ftyp box.

$mime = mime_content_type('image.hej2');
echo $mime; // application/octet-stream or image/heif

File Detection Steps

How to programmatically detect a image/hej2k file by reading its raw bytes:

1 Check for ISOBMFF 'ftyp' box starting at byte offset 4
2 Verify 'j2ki' brand string starting at byte offset 8 to confirm HEIF encapsulation of JPEG 2000

Software Support

K

Kakadu Software

O

OpenJPEG

G

Grok

Conversion Tools

Share & Embed

Markdown Badge

[![HEJ2K Format](https://freewebptojpg.com/mime/image/hej2k/badge.svg)](https://freewebptojpg.com/mime/image/hej2k)

Interactive iframe Widget

<iframe src="https://freewebptojpg.com/mime/image/hej2k/embed" width="100%" height="280" style="border:1px solid #cbd5e1;border-radius:8px;" title="HEJ2K Specs"></iframe>

JSON API

All data on this page is available as a free, open JSON API. Use it in your project, documentation, or tooling.

GET https://freewebptojpg.com/mime/image/hej2k.json Open JSON

Free to use

No auth required

CORS enabled

Use from any domain

Cached 24h

Cache-Control headers set

Frequently Asked Questions

What is the difference between image/jp2 and image/hej2k?

While both formats encode image data using the JPEG 2000 standard, image/jp2 uses the traditional JP2 file format. In contrast, image/hej2k encapsulates the JPEG 2000 codestream within the modern HEIF (ISOBMFF) container, allowing for richer metadata, auxiliary image items, and depth maps.

What is the magic byte for HEJ2K?

Like other HEIF files, HEJ2K uses the ISOBMFF structure. It begins with a 4-byte box size, followed by the 'ftyp' identifier and the brand 'j2ki'. In hex, this is commonly XX XX XX XX 66 74 79 70 6A 32 6B 69 (....ftypj2ki).

Are HEJ2K images supported in web browsers?

No. There is no native web browser support for JPEG 2000 images encapsulated in HEIF containers. These files are typically used in specialized archival, medical, or geospatial workflows.