3dl

3dl is the common file extension for a three-dimensional look-up table (3D LUT) used in color management and color grading. A 3D LUT maps input RGB colors to output RGB colors by applying a color transformation across a three-dimensional grid, enabling consistent color appearances across devices and workflows.

The 3dl format is typically an ASCII text file. The first portion usually contains a header that identifies the LUT size, such as a line indicating the 3D size (for example, LUT_3D_SIZE 33). Following the header, lines provide three floating-point numbers that represent the transformed red, green, and blue values for each entry in the color grid. The entries are arranged in a fixed order that depends on the specific implementation (for instance, varying fastest along one color channel before the next).

Usage and interoperability: 3dl LUTs are loaded by many color grading, compositing, and video editing applications to apply a predefined color transformation to images or footage. They are often created with LUT generation tools or exported from color grading sessions and can be converted to other formats (such as .cube or .lut) to improve compatibility across software.

History and context: The .3dl extension represents an early, widely used 3D LUT format that circulated in film, broadcast, and digital imaging pipelines. While newer LUT formats have emerged, the 3dl format remains in use in various ecosystems and can be supported directly or through conversion tools.

See also: LUT, 3D LUT, color grading, OpenColorIO, .cube, .lut.