HDR file format: what it is and how to use it

Radiance HDR stores real scene light in a clever shared-exponent pixel, the classic format behind HDRI environment maps and lighting research. Learn when to use it and what to choose instead.

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What is a HDR file?

An .hdr file is a high-dynamic-range image in Greg Ward's Radiance format (1989): each pixel stores RGB plus a shared exponent byte (RGBE), squeezing real-world luminance into ~32 bits per pixel with optional RLE. It was the format that put HDRI on the map: captured light you could use to illuminate a render.

When should you use .hdr?

  • Environment maps: sky, studio and interior HDRI for image-based lighting.
  • Lighting research: the format decades of papers and datasets were published in.
  • Small HDR storage: RGBE packs wide range into fewer bytes than float formats.

When is another format a better fit?

For VFX pipelines with channels and layers, EXR is the professional successor. For raw float data in research PFM is simpler; for display images, tone-map to PNG or JPG, since .hdr's range is wasted on screens anyway.

The short version: .hdr is the classic HDRI container, still the default for environment maps but superseded by EXR for production work.

How to open a HDR file

On Windows

Double-click the file, or open it with Adobe Photoshop.

On macOS

Blender opens HDR files on macOS.

In your browser

Open HDR files right in a browser tab or with the dexrr viewer. No install, no upload.

Also opens in

  • Adobe Photoshop
  • Blender
  • GIMP
  • Luminance HDR

View or convert HDR files

A quick preview or a new format. No install, no upload.

View HDR files Preview and inspect HDR files Convert to HDR Turn files into HDR HDR to EXR OpenEXR HDR to PFM Portable Float Map HDR to TIFF Tagged Image File Format

HDR technical details

Full name
Radiance HDR (RGBE)
Extensions
.hdr .rgbe .pic
MIME type
image/vnd.radiance, image/x-hdr
Magic bytes
23 3F 52 41 44 49 41 4E 43 45 (#?RADIANCE)
Compression
Lossless
Developer
Greg Ward (Radiance)
Specification
www.radiance-online.org

HDR questions, answered

How do I open a .hdr file?

Blender, Unreal, Unity, Photoshop, GIMP and HDR viewers read it. dexrr displays and converts hdr files in your browser.

Can I convert HDR files online?

Yes, dexrr converts hdr locally in your browser: HDR to PNG with tone mapping or HDR to EXR for production pipelines.

Is .hdr better than .exr?

For a single environment map it is smaller and simpler; for production EXR's channels, float precision and tooling make it the professional pick.

Why does my .hdr image look washed out?

Viewers often apply a naive gamma. It is scene-linear data, so apply tone mapping or an sRGB transform to see it correctly.

Is the HDR format outdated?

It is elderly but entrenched, still the default interchange for HDRI environment maps across 3D tools.