What is a .cube LUT file? 17, 33 and 65 point LUTs explained, with a look inside the file

Updated 2026-09-24 · 5 min read · by Nunik Co.

A LUT is the most used and least understood file in video colour. This is the whole thing in five minutes, including what is inside the file when you open it in a text editor.

What a lookup table does

Every pixel in your footage is a red, green and blue value. A 3D LUT is a table that says, for a grid of input RGB values, what output RGB value to produce. Your editor looks up each pixel's colour in the table and replaces it. That is it. No adjustment layers, no sliders, no maths at playback beyond finding the nearest grid points and blending between them.

Because the table maps colours independently, a LUT can do things sliders cannot: shift one hue without touching its neighbours, bend the shadows blue while leaving highlights warm, reproduce a film stock's non linear response. That is why film emulations and reference matches ship as LUTs.

1D versus 3D

A 1D LUT has three separate curves, one per channel. Each channel is adjusted on its own, so it can change contrast and colour balance but cannot change one colour based on another. A 3D LUT has a single cube where every combination of R, G and B maps to its own output. Creative looks are almost always 3D. The .cube format can hold either; the header tells you which.

What 17, 33 and 65 mean

The number is the grid size along each axis. A 33 point LUT samples 33 red values, 33 green and 33 blue, giving 33 cubed, or 35,937, entries. Colours between grid points are interpolated.

Bigger is not automatically better. A 65 point LUT built from a noisy match carries the noise into the grade at higher resolution. ChromaMimic offers all three and defaults to 33.

Inside the file

A .cube is plain text. Open one and you will see something like this:

TITLE "ChromaMimic match"
LUT_3D_SIZE 33
DOMAIN_MIN 0.0 0.0 0.0
DOMAIN_MAX 1.0 1.0 1.0
0.000000 0.000000 0.000000
0.031250 0.000000 0.000000
0.062500 0.000000 0.000000
...

After the header comes one line per grid entry: the output R, G and B for that input point, as decimals from 0 to 1. The lines are ordered with red changing fastest, then green, then blue. So the first 33 lines walk red from black to full red with green and blue at zero, the next 33 do the same with green one step up, and so on for all 35,937.

The DOMAIN lines are optional and almost always 0 to 1. Comments start with #. That is the entire format, which is why nearly every tool reads it.

Which software reads .cube

DaVinci Resolve, Premiere Pro, After Effects, Final Cut Pro, Avid Media Composer, Photoshop (as a Color Lookup adjustment layer), CapCut, OBS, most camera monitors and most colour plugins. Lightroom and Camera Raw read it only inside a profile. How to do that.

What a LUT does not know

A LUT maps colours. It does not know what colour space the input is in. A LUT built for Rec.709 applied to S-Log3 produces a flat, milky image, because the input values mean something different. Convert first, then apply. This is the most common LUT problem there is.

Spotting a broken one

• No LUT_3D_SIZE line: not a 3D cube file.
• The wrong number of lines after the header (size cubed): truncated download.
• Values outside 0 to 1, or the word NaN: a generator that did not guard its maths. ChromaMimic clamps values and replaces any invalid entry with identity, so its files never contain either.
• Ends in .cube.txt: rename it.

Make one

ChromaMimic writes a standard Adobe Cube v1.0 file from an original frame and a reference still, in your browser, at 17, 33 or 65 points. Open the result in a text editor and you will see exactly the structure above.