In the film industry, 3D LUTs (lookup tables) are used to calculate preview colors for a monitor or digital projector of how an image will be reproduced on the final film print. A 3D LUT is a 3D lattice of output color values. Each axis is one of the 3 input color components and the input color thus defines a point inside the lattice. Since the point may not be on a lattice point, the lattice values must be interpolated; most products use trilinear interpolation.
Cubes may be of various sizes and bit depths. Often 17x17x17 cubes are used as 3D LUTs. The most common practice is to use RGB 10bit/component log images as the input to the 3D LUT. Output is usually RGB values that are to be placed unchanged into a display device's buffer.
Modern graphics cards have direct support for 3D LUTs, allowing entire HD images to be processed at 60fps or faster.