3D LUT · apply and export .cube files

A LUT is a colour lookup table: it maps every original colour to another one. Film grades, camera-maker film simulations, presets you bought online — underneath they're all this same table, which is why one LUT applied to different photos yields a consistent look. That consistency is exactly what makes it less work than grading by hand.

Applying: take Image > Color Lookup (3D LUT)…, pick a `.cube` file, and it lands on the active image layer through trilinear interpolation. Parsing is strict: the file must carry `LUT_3D_SIZE` and exactly size³ rows of data, and anything that does not line up is refused outright — better to reject a file than to hand you a miscomputed grade. Exporting: take File > Color Lookup…, and every visible adjustment layer in the document is run over an identity color lattice, bottom of the stack upward, and baked into a single 33×33×33 `.cube`; adjustment layers inside a layer group are not counted, so move one out of its group if you want it included. The way to use that: grade here with curves, levels, and hue/saturation until it looks right, then export one LUT and apply it to a whole clip in an editing suite. One thing to know upfront: with no adjustment layers in the document, what you get is an identity LUT — the one that changes nothing. That is not a broken export; there was simply nothing to bake. There are also 10 built-in looks plus “Original” (Color Lookup under new adjustment layer) like Teal-orange, Faded film, and Black-gold, but they are a luminance-gradient approximation, not true 3D LUTs: a real 3D LUT can do cross-channel interaction (red pulling green around), and a luminance mapping cannot. For that, load an actual `.cube`. It all runs in your own browser and the LUT file is never uploaded; while you're signed out the image isn't either, and once you sign in your work is saved automatically to your own cloud projects.