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What is Tone Mapping?

Tone mapping converts luminance and color from a wide dynamic range into values an output display or image format can reproduce. The transformation seeks to retain useful detail and perceptual contrast.

How Tone Mapping works

A tone-mapping stage applies a transfer from scene or source luminance into the smaller range available to a target, often with accompanying color-volume handling. Global operators use one mapping across the image, whereas local operators adapt to surrounding detail and can alter spatial contrast. The result is an artistic and technical rendering rather than a reversible packing step. It belongs near color conversion when HDR masters produce SDR displays, previews, or derivatives.

Key facts

  1. Global tone curves are predictable and inexpensive, while local operators can preserve detail in bright and dark neighborhoods but may create halos or unstable changes between video frames.
  2. Correct processing depends on interpreting the source transfer function, primaries, mastering assumptions, and target display; treating encoded values as linear light can distort contrast and color.
  3. Inverse tone mapping can expand an SDR signal for HDR presentation, but clipped highlights and quantized shadow detail are not restored simply because the output has a wider luminance range.

When Tone Mapping matters

Apply tone mapping when producing SDR derivatives from HDR images or video for incompatible displays. An unsuitable operator or metadata assumption can clip highlights, crush shadows, or shift colors.

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