How the Radiance RGBE Format Works
RGBE stores each pixel as four bytes: one for each of red, green, and blue mantissa values, plus a shared exponent byte. This gives the format a dynamic range of approximately 1038- Far exceeding the 0–255 range of standard 8-bit formats. The file uses run-length encoding for compression.
Primary Use: Image-Based Lighting (IBL) in 3D
HDR environments are used extensively in 3D rendering and CGI as image-based lighting (IBL) maps. A spherical HDR panorama of a scene is projected onto a dome or sphere around a 3D object; the renderer samples this map to compute realistic reflections and ambient illumination. Engines and renderers such as Blender, Unreal, V-Ray, and Arnold all consume .hdr files natively.
Why Converting JPG to HDR Is Experimental
A standard JPEG stores luminance in 8 bits per channel (0–255). Converting it to .hdr repackages that data in the HDR container but does not add dynamic range that was never captured. The output is a valid .hdr file that will open in 3D software, but its lighting values will be limited to the 0–1 range of the source JPEG. This is why the format is marked experimental- Use cases are narrow and results are often not what users expect.
Where Genuine HDR Content Comes From
True HDR images are captured by exposure bracketing (merging multiple exposures at different EVs in software like Photomatix or Lightroom), or directly from cameras with high-dynamic-range sensors processing RAW files at 16-bit depth. Dedicated 360° HDR panorama cameras are also common in 3D production pipelines.