What is a .hdr file?
High Dynamic Range Image · Image · Greg Ward (Radiance) · 1989
A Radiance .hdr file is a high dynamic range image that stores a far wider range of brightness than an ordinary photo. It is used in 3D rendering and photography for realistic lighting and environment maps.
What is a .hdr file used for?
HDR files begin with the text header #?RADIANCE and store each pixel with a shared exponent (the RGBE encoding), capturing detail from deep shadows to bright highlights that an 8-bit image would clip.
In 3D software, .hdr environment maps light a scene realistically. It opens in Photoshop, GIMP and 3D tools; note that .hdr is also used, unrelated, for some game and installer data.
How to open a .hdr file
The .hdr format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list. For a step-by-step walkthrough, see how to open a .hdr file.
Windows
- Adobe Photoshop
- GIMP
- Blender
- Luminance HDR
macOS
- Adobe Photoshop
- GIMP
- Blender
Linux
- GIMP
- Blender
- Luminance HDR
How to convert a .hdr file
You can convert a .hdr file to exr, png, jpg, tiff using a conversion tool or the export menu of an app that opens it.
.hdr file signature (magic bytes)
Programs recognise a .hdr file by the bytes at the start of the file, not by its name. These are the signatures for Radiance HDR. For a full breakdown, see the Radiance HDR file signature page.
| Hex signature | Offset | Note |
|---|---|---|
| 23 3F 52 41 44 49 41 4E 43 45 | 0 | '#?RADIANCE' |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .hdr file?
A Radiance .hdr file is a high dynamic range image that stores a far wider range of brightness than an ordinary photo. It is used in 3D rendering and photography for realistic lighting and environment maps.
How do I open an .hdr image file?
Use Photoshop, GIMP or Blender, all of which read Radiance HDR. Tone-mapping tools like Luminance HDR convert it to a normal image.
What is an HDR file used for?
Storing high dynamic range images, especially environment maps that light 3D scenes realistically, and merged HDR photographs.
What is the difference between HDR and EXR?
Both hold high dynamic range images. Radiance HDR is older and simpler; OpenEXR supports more channels and higher precision and is the film and VFX standard.
Related formats
Sources
Details on this page were checked against authoritative references: