LUTs

Look-up table (LUT) is a data structure used to transform a set of input values to a corresponding set of output values. In digital imaging and video, LUTs are most often used to convert color values from one color space or look to another, implement gamma and tone mapping, or apply creative color grades. A LUT encodes a function that, given an input color, yields an output color, allowing complex transforms to be precomputed for fast replay in software or hardware.

There are two common types: 1D LUTs and 3D LUTs. A 1D LUT stores a mapping for each channel (R, G, or B) separately and is typically used for gamma corrections or simple tone curves. A 3D LUT stores a mapping from RGB triples to new RGB values and can encode complex color relationships and cross-channel effects. 3D LUTs are widely used for color grading and color space conversions; their typical sizes are 17x17x17, 33x33x33, or 64x64x64 samples.

LUTs can be represented in various formats, including text-based cube files (.cube), binary .3dl, or proprietary formats. They are used in post-production pipelines, game engines, and display calibration workflows. Real-time systems load a LUT and apply it to each pixel during rendering or playback, usually after primary color corrections or as part of a display transform.

When using LUTs, it is important to consider input and output color spaces, clipping and gamut, interpolation quality, and the intended workflow to ensure predictable results across devices.