Tone Curve
A graph mapping input luminance values to output values. It is the most powerful tonal adjustment tool for precisely controlling brightness, contrast, and tonal distribution in images.
A tone curve is a graphical representation of a function that maps each pixel's input value (horizontal axis) to an output value (vertical axis). A straight 45-degree diagonal represents identity. Reshaping this curve adjusts brightness, contrast, and tonal distribution.
- S-curve: Darkens shadows and brightens highlights, steepening the midtone slope and raising midtone contrast
- Inverse S-curve: Reduces contrast for a flat, film-like aesthetic
- Per-channel manipulation: Adjusting RGB channels independently enables color cast correction and creative grading. Lifting the red channel's shadows introduces warmth into dark areas
- Clipping: Moving endpoints inward crushes tonal range to pure white or black
Connecting control points via spline interpolation helps reduce banding. In video post-production, curves are baked into LUTs (Look-Up Tables) for real-time playback, applying complex transformations as simple array lookups per pixel.