HDRi

HDRI stands for High Dynamic Range Imaging. It refers to techniques and file formats that capture, process, or display a broader range of luminance than conventional digital imaging. In photography, HDRI typically involves capturing several photographs of the same scene at different exposure levels and combining them to preserve both highlights and shadows. The resulting HDR image stores radiance values rather than a single tone-mapped brightness, enabling later tone mapping to display on standard monitors or to be used for archival purposes.

In computer graphics, HDRI commonly refers to the use of high dynamic range images as environment maps to illuminate scenes and provide reflections. Common formats include Radiance HDR (.hdr) and OpenEXR (.exr). Projections such as equirectangular and cube maps are used for 360-degree panoramas and other lighting tasks. When used as image-based lighting (IBL), the HDRI provides incident light and accurate reflections that respond to scene geometry and materials, enabling more physically plausible rendering within PBR pipelines.

History: The concept emerged in the late 1980s and 1990s, with foundational work by Paul Debevec and Jitendra Malik on recovering and representing scene radiance, notably the 1997 paper “Recovering High Dynamic Range Radiance Maps from Images.” HDRI has since become widely supported in consumer cameras, software, game engines, and digital imaging workflows.

Practical considerations: In photography, proper bracketing, alignment, and processing are required to avoid artifacts; tonemapping is used to display HDR images on usual displays. In CGI, the resolution and projection of the HDRI, as well as the sampling of lighting, affect realism and performance.