HDR vs EXR: Radiance RGBE vs OpenEXR High Dynamic Range Formats
A technical comparison between Greg Ward's Radiance HDR (.hdr / RGBE) and ILM's OpenEXR (.exr). Explore shared exponents, half-float pixels, multi-layer rendering, and tone mapping.
Radiance HDR (.hdr / .pic) pioneered 32-bit RGBE high dynamic range imaging for architectural lighting simulation and skyboxes. OpenEXR, developed by Industrial Light & Magic (ILM), is the visual effects industry standard supporting 16-bit half float, 32-bit float, deep data, and multi-channel layer compositing.
| FEATURE | HDR | EXR |
|---|---|---|
| Color Encoding | 32-bit RGBE (8-bit R, G, B + 8-bit shared exponent) | 16-bit half or 32-bit full float per channel |
| Multi-Layer / Channels | RGB only (single layer) | Arbitrary channels and multi-part layers |
| Compression | Adaptive Run-Length Encoding (RLE) | PIZ, ZIP, ZIPS, RLE, B44, DWAA, DWAB |
| Decoder Footprint | Lightweight (~200 lines of pure code) | Heavy (requires OpenEXR C++ library / WASM) |
| Primary Domain | Environment maps, game lighting, WebGL skyboxes | Film VFX, CGI rendering, and multi-pass compositing |
- Compact 32-bit per pixel RGBE representation with shared 8-bit common exponent
- Broad support across real-time 3D graphics engines (Three.js, Babylon.js, Unity, Unreal)
- Simple byte-stream RLE compression with fast CPU decoding without heavy library dependencies
- Universal format for HDRI 360-degree environment lighting and background panorama maps
- Native 16-bit half-float and 32-bit float channels offering superior numerical precision
- Supports arbitrary multi-layer rendering passes (Diffuse, Specular, Normal, Z-Depth, Cryptomatte)
- Lossless (ZIP, PIZ, RLE) and lossy (B44, DWA, DWAB) modern compression algorithms
- Definitive VFX and animation industry standard across Nuke, DaVinci Resolve, Blender, and Maya
Use OpenEXR when rendering 3D CGI scenes, VFX multi-pass composites, and cinematic color grades requiring extreme floating-point dynamic range. Use Radiance HDR for fast, lightweight WebGL skyboxes and 360-degree environment textures, or convert HDR maps to tone-mapped PNG for instant in-browser viewing and web deployment.
Converting files between HDR and EXR frequently? The convrtr Chrome Extension lets you right-click any image on any webpage or open the Side Panel to convert assets instantly using local WebAssembly with zero server uploads.