Tonemapping

Tonemapping is a class of image processing techniques used to convert high dynamic range (HDR) imagery into a displayable low dynamic range, suitable for standard monitors and prints. The goal is to preserve perceptual cues such as overall contrast, important details, and color relationships, so that the result looks natural on devices with limited dynamic range. Tonemapping is widely used in computer graphics, photography, and visualization, where scenes may contain radiance values far beyond what a display can reproduce.

The typical workflow starts with an HDR image in a linear color space. The luminance component is extracted or computed, and a tonemapping operator is applied to map scene luminance to display-referred values. Color is then scaled or adjusted to fit within the display gamut, and gamma correction or other perceptual adjustments may be applied to finalize the image. Operators can be global, applying the same mapping to every pixel, or local, adapting the mapping based on neighboring pixel values to preserve local contrast and texture. Local methods often use edge-preserving filters to reduce halos and preserve detail in bright or shadow regions.

Common tonemapping operators include global approaches that compress the entire dynamic range with a fixed curve, such as Reinhard or Drago-style mappings, and local approaches that emphasize local contrast and detail through adaptive filtering and exposure control. Filmmic and perceptually motivated curves are also used to produce more cinema-like results. Practical use involves balancing luminance, color saturation, and artifacts such as halos, with the chosen operator influenced by the material and viewing conditions.