OpenAnyFile
The short version: HDR is a Radiance HDR Image from Greg Ward, Lawrence Berkeley Lab. The longer version — including the quirk that trips most people up — is below, along with a viewer that runs entirely on your own device.
Radiance HDR Image is an image format developed by Greg Ward, Lawrence Berkeley Lab, first appearing in 1989. It is normally produced by 3D renderers, HDRI environment libraries.
Uses RGBE encoding — three colour bytes plus one shared exponent byte — to hold an enormous dynamic range in 32 bits per pixel. Most .hdr files are lighting environments rather than photographs.
| Full name | Radiance HDR Image |
|---|---|
| File category | Images |
| MIME type | image/vnd.radiance |
| Magic bytes (file signature) | 23 3F 52 41 44 49 41 4E 43 45 (#?RADIANCE) |
| Developer | Greg Ward, Lawrence Berkeley Lab |
| Introduced | 1989 |
| Usually created by | 3D renderers, HDRI environment libraries |
| OpenAnyFile engine | progressive image decoder |
| Opens without upload | Yes — parsed locally in your browser |
OpenAnyFile routes .hdr to its progressive image decoder, which renders the picture drawn natively if your browser ships a decoder for this codec, and a full byte-level inspection with the detected signature if it does not.
Viewing, inspecting and verifying. You get the picture drawn natively if your browser ships a decoder for this codec, and a full byte-level inspection with the detected signature if it does not. File details, exact byte size and the detected signature are always shown.
Guaranteed rendering. Whether the picture draws depends on whether your browser ships a decoder for this codec; when it does not, you still get the full byte-level inspection instead of an error.
Plenty of sites promise they delete your uploads. OpenAnyFile avoids the promise by avoiding the upload. When you drop a .hdr file in, the browser grants the page temporary read access to those bytes and nothing more — the page has no path to send them anywhere. You can verify it in seconds: open DevTools, switch to the network tab, and open a file. The request list stays empty.
Yes. OpenAnyFile's progressive image decoder runs in your browser, so you can read a HDR file with nothing installed. You get the picture drawn natively if your browser ships a decoder for this codec, and a full byte-level inspection with the detected signature if it does not. For full editing you still need the original application — this is a viewer, not an editor.
Look at the first bytes rather than the extension. A genuine HDR begins with 23 3F 52 41 44 49 41 4E 43 45 (#?RADIANCE). Opening the file in OpenAnyFile shows that signature in the file-details panel, so a file renamed to .hdr by mistake is easy to spot.
With OpenAnyFile, yes, because nothing is uploaded. The file is read locally through your browser's File API and never leaves your device, so there is no server copy to leak, log or retain. That matters most for the kind of file people are least willing to hand to a random converter site.
Radiance HDR Image — an image/vnd.radiance format created by Greg Ward, Lawrence Berkeley Lab since 1989. Uses RGBE encoding — three colour bytes plus one shared exponent byte — to hold an enormous dynamic range in 32 bits per pixel. Most .hdr files are lighting environments rather than photographs.
Yes — the same engine also opens .emf, .exr, .jp2, so you can compare related files without switching tools.
These open with the same engine, so if you have one of these sitting next to your .hdr file, it will open too: