.hdr File — Radiance HDR Image

HDR (High Dynamic Range) files in Radiance RGBE format store images with a wide luminance range that exceeds the capabilities of standard 8-bit images. Developed by Greg Ward for the Radiance lighting simulation system in the late 1980s, the format encodes each pixel as three 8-bit mantissas and one shared 8-bit exponent, efficiently representing a broad range of light intensities in only 32 bits per pixel. HDR images are primarily used as environment maps for image-based lighting in 3D rendering, where they provide realistic light probes that illuminate virtual scenes with captured real-world illumination. The format is widely used in architectural visualization, product rendering, visual effects, and game development for skyboxes and reflection maps. HDR panoramic images, often captured as equirectangular projections, are essential for physically-based rendering workflows. While OpenEXR has become more common for VFX production work, Radiance HDR remains popular for environment maps due to its smaller file sizes and widespread support in 3D applications, game engines, and online HDR image libraries.