How AgX generates its bundled LUTs

AgX bundles a set of .cube LUTs derived from film-emulation parameters. The agx-lut-gen crate produces these as a build step. This page explains the design choices behind the generation process — why the LUTs are pre-built rather than computed at runtime, and what the parameters mean.

AgX ships a set of generated .cube LUTs used by the e2e test pipeline and as starting points for film-emulation looks. The generator lives in the agx-lut-gen crate (crates/agx-lut-gen/); the bundled outputs live in crates/agx-e2e/fixtures/looks/luts/.

The generator is a small Rust binary that, for each named LUT, evaluates a transformation function over a regular 3D grid in input RGB and writes the result as a .cube file. The current set splits into two categories:

  • Film stocks: Portra 400, Kodachrome 64, Cinestill 800T, Tmax 100, Tri-X 400.
  • Stylistic looks: Blade Runner, Cinema Warm, Dune, Faded BW, High Contrast BW, Neo Noir.

Why generate LUTs in code rather than authoring them in a colorist tool:

  • Reproducibility. Each LUT is the deterministic output of a versioned function. Bug fixes or design changes propagate by re-running the generator.
  • Test stability. The e2e suite compares rendered output against committed golden images. A regenerated LUT that introduces unintended color shifts shows up as a visual diff in the test suite.
  • Onboarding. Contributors can read the generator source to understand how each look is constructed, rather than treating each LUT as an opaque file.

See also