Clut

CLUT stands for Color Look-Up Table. It is a data structure used in digital imaging and computer graphics to transform color values, enabling recoloring, color correction, and artistic color grading. A CLUT maps input color components to output components, allowing complex color transforms to be applied efficiently, often in real time.

There are two common forms: 1D LUTs and 3D LUTs. A 1D LUT stores a mapping for a single color channel (red, green, or blue) and is used for gamma correction, brightness adjustments, or linearization. A 3D LUT stores mappings for combinations of R, G, and B and is typically organized as an N x N x N grid. Common sizes are 17, 33, or 64 per dimension, with each grid point containing an output RGB triplet. Colors falling between grid points are estimated by interpolation, most often trilinear interpolation.

Applications of CLUTs include color grading for film and video, display calibration, and various image processing pipelines. In real-time graphics, 3D CLUTs are frequently implemented as textures that are sampled in fragment shaders to apply a color transformation to each pixel.

Formats and storage vary. 3D LUTs are commonly saved in file formats such as .cube, .3dl, or .lut, and may be embedded in software pipelines as binary data. A related concept is the palette or indexed-color CLUT, where an image stores color indices that reference a separate palette of actual colors; this is common in older graphics systems and certain image formats. CLUTs provide a compact, flexible method for consistent color transformation across images and media.