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.
What opens 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.
Windows
- Adobe Photoshop
- GIMP
- Blender
- Luminance HDR
macOS
- Adobe Photoshop
- GIMP
- Blender
Linux
- GIMP
- Blender
- Luminance HDR
Open a .hdr file step by step
- Confirm the file really is a .hdr. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Adobe Photoshop or GIMP.
- On Mac, use Adobe Photoshop or GIMP.
- On Linux, try GIMP or Blender.
- Still stuck? Convert the .hdr to exr, which opens more widely.
Why can't I open my .hdr file?
Almost always because no installed app understands Radiance HDR. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .hdr at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
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.
What is the .hdr file signature (magic bytes)?
A .hdr file starts with the hex bytes 23 3F 52 41 44 49 41 4E 43 45, which read as #?RADIANCE in ASCII. Programs identify Radiance HDR by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for Radiance HDR. For a full breakdown, see the Radiance HDR file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 23 3F 52 41 44 49 41 4E 43 45 | 0 | #?RADIANCE | '#?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
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