Radiance HDR file signature
Magic number at the start of the file · #?RADIANCE
A Radiance high dynamic range image opens with the ASCII text #?RADIANCE, the first line of a small text header that precedes the RGBE-encoded pixels.
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 23 3F 52 41 44 49 41 4E 43 45 (the text #?RADIANCE), it is a Radiance HDR file.
What each byte of 23 3F 52 41 means
Here is the signature byte by byte, the way a hex editor shows it: the position in the file, the value in hex and in decimal, and the character that value stands for in ASCII. Bytes with no printable character show a dot.
| Byte offset | Hex | Decimal | ASCII |
|---|---|---|---|
| 0 | 23 | 35 | # |
| 1 | 3F | 63 | ? |
| 2 | 52 | 82 | R |
| 3 | 41 | 65 | A |
| 4 | 44 | 68 | D |
| 5 | 49 | 73 | I |
| 6 | 41 | 65 | A |
| 7 | 4E | 78 | N |
| 8 | 43 | 67 | C |
| 9 | 45 | 69 | E |
Formats that use the 23 3F 52 41 signature
These file types in our database carry this signature:
How to check a file's signature
You can read the bytes of any file yourself. They are shown in hex, the same way this page lists them.
Linux & macOS
- xxd -l 16 example.hdr
- hexdump -C -n 16 example.hdr
- file example.hdr
Windows (PowerShell)
- Format-Hex -Path example.hdr -Count 16
Python
- open("example.hdr","rb").read(10).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the Radiance HDR file signature?
Radiance HDR files start with the hex bytes 23 3F 52 41 44 49 41 4E 43 45 (#?RADIANCE 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.hdr on Linux or macOS, or Format-Hex -Path example.hdr -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the Radiance HDR signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine Radiance HDR file has these exact bytes; a file with the wrong bytes is not really Radiance HDR, whatever its name says.
Related signatures
Sources
Reuse this signature
This entry is part of the WhatFileType file signature reference, published under a CC BY 4.0 licence with the full provenance for every entry, a copy-paste embed and a JSON export. Credit WhatFileType and the data is yours to republish.