HDRTonmapping

HDR tonemapping is the process of converting high dynamic range (HDR) imagery, which encodes a wide range of luminance values, to a representation that can be displayed on devices with more limited dynamic range. The goal is to preserve important scene detail and contrast while fitting the luminance into the display’s capabilities. Tonemapping is a key step in HDR imaging pipelines, used for both rendering scenes and preparing content for standard (non-HDR) displays.

Tonemapping operators (TMOs) come in global and local varieties. Global operators apply a single mapping function to all pixels, producing consistent compression of luminance; examples include simple logarithmic or power-law mappings and the Reinhard-style operator. Local operators modify the mapping based on a pixel’s neighborhood to preserve local contrast and edge detail, often using multi-scale or edge-aware techniques. Color and gamut management may accompany the luminance mapping to maintain natural color appearance.

Practical considerations include the choice of perceptual color space, white point, and gamma, as well as display characteristics such as peak luminance and color gamut. Temporal coherence is a concern for video, since abrupt changes between frames can cause flicker or halos with some TMOs. Some approaches operate in log-luminance or LMS space to align with human vision and reduce artifacts.

The evaluation of tone-mapping quality combines subjective viewing studies with objective metrics such as TMQI. HDR tonemapping is widely used in photography, film, and computer graphics to render scenes for dynamic displays and to enable consistent appearance across viewing conditions.