JPEG 2000 file signature
Magic number at the start of the file · ....jP ....
The JPEG 2000 signature box is a fixed 12-byte sequence: a box length of 12, the box type jP followed by two spaces, then a CRLF, 0x87 and LF that guard against transfer corruption.
What this magic number means
A magic number is a short, fixed run of bytes at a known position that tells a program what a file really is, no matter what the filename says. If a file starts with the bytes 00 00 00 0C 6A 50 20 20 0D 0A 87 0A (the text ....jP ....), it is a JPEG 2000 file.
Formats that use the 00 00 00 0C signature
These file types in our database carry this signature:
How to check a file's signature
You can read the first bytes of any file yourself. The magic bytes are shown in hex, the same way this page lists them.
Linux & macOS
- xxd -l 16 example.jp2
- hexdump -C -n 16 example.jp2
- file example.jp2
Windows (PowerShell)
- Format-Hex -Path example.jp2 -Count 16
Python
- open("example.jp2","rb").read(12).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the JPEG 2000 file signature?
JPEG 2000 files start with the hex bytes 00 00 00 0C 6A 50 20 20 0D 0A 87 0A (....jP .... in ASCII). This magic number identifies the format regardless of the file's name or extension.
How do I check a file's magic number?
Open the file in a hex editor, or run a command such as xxd -l 16 example.jp2 on Linux or macOS, or Format-Hex -Path example.jp2 -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the JPEG 2000 signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine JPEG 2000 file has these exact bytes; a file with the wrong bytes is not really JPEG 2000, whatever its name says.