CLUTs

CLUT stands for color look-up table. It is a data structure that encodes a mapping from input color values to output color values. CLUTs are used in image and video processing to implement color quantization, color space conversions, gamma correction, and color grading by replacing each input color with a precomputed output color. They enable fast, per-pixel color remapping at the cost of fixed precision and memory.

Two common forms are 1D and 3D CLUTs. A 1D CLUT maps a single channel (for example, a luminance or a color channel) to its output value and is typically used for simple gamma or intensity adjustments. A 3D CLUT maps a triplet of input color coordinates (usually RGB) arranged on a regular grid with N x N x N entries. Each entry provides the corresponding output color (often in RGB). The grid may be a small table (for example, 17^3) or a larger table (such as 32^3 or 33^3).

Because input colors rarely fall exactly on grid points, interpolation is typically applied to derive the final color. Trilinear interpolation is common for 3D CLUTs; linear interpolation is used for 1D CLUTs. Some systems also employ dithering or error diffusion to reduce quantization artifacts.

Uses include classic indexed-color images and palettes (8-bit graphics), real-time video pipelines and color-grading workflows, and display calibration where 3D LUTs encode transformations from camera-referenced color spaces to display-referred spaces. In modern software, CLUTs are often implemented as textures or arrays that can be loaded and reused by graphics pipelines.

See also: Look-up table, color space, color grading, ICC profile.