BLUT File

What are BLUT files and how to open them

Are you having problems opening a BLUT file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your BLUT files.

What is a BLUT file?

A .BLUT file is a Houdini Binary LUT file.

Houdini LUTs in binary form store color-lookup tables for SideFX Houdini. They provide color correction data - either 1-dimensional (adjusting individual channels like red, green, blue or alpha) or 3-dimensional ("color cube") transformations - used when viewing, compositing, or exporting images. Houdini writes them when a user builds color correction in a compositing network and chooses "Save LUT" in either ASCII or binary form using the native LUT saving tools.

Binary LUTs are faster to load and take up less disk space than the ASCII LUT counterpart, but are harder to read or edit manually after saving. Houdini's PXL_Lookup class handles both, allowing creation, evaluation, and application of LUTs within Houdini, including saving in binary (.blut) when the user requests that format.

Internally the file begins with a 4-byte magic sequence of ASCII characters: H L U T. After that comes a header with fields in big-endian order (since Houdini expects that in its binary LUTs). The header includes a version number (e.g. 1 for linear 1D LUT, 2 for linear 3D, 3 for log or prelut), entries defining which channels are affected (R, G, B, A, RGB, RGBA, etc.), input domain range ("From … To …"), black and white points, LUT size (number of entries for 1D, cube dimension for 3D), and a byte specifying floating-point precision ('h' for 16-bit float or 'f' for 32-bit). Following the header is the raw LUT data as signed or unsigned floats per the precision field, with one or more tables (for 1D) or a color cube of dimension³ entries (for 3D).

How to open BLUT files

Important: Different programs may use files with the BLUT file extension for different purposes, so unless you are sure which format your BLUT file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: August 24, 2026

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