What is a LUT?

The one-sentence version

A LUT is a colour transform written down as a table instead of a formula. Give it a red, green and blue value; it hands back a different red, green and blue value. That is all a LUT can do — but because it can do it to any colour, a well-built table can reproduce the behaviour of a camera's colour science, a film stock, or a grade a colorist spent a day on.

1D LUT vs. 3D LUT

A 1D LUT is three independent curves: one for red, one for green, one for blue. It can change brightness, contrast and channel balance, but it cannot change one colour without changing every colour that shares a channel value. A 1D LUT can make an image warmer; it cannot turn only the blues teal.

A 3D LUT treats the colour as a point inside a cube whose axes are R, G and B. Every grid point in the cube stores its own output colour, so any input colour can be sent anywhere. This is why creative looks, film emulations and camera conversions are almost always 3D LUTs.

Grid size	Entries	Typical use
17 × 17 × 17	4,913	Quick previews, older hardware
25 × 25 × 25	15,625	Many creative looks
33 × 33 × 33	35,937	The common standard for .cube files
65 × 65 × 65	274,625	Camera manufacturer conversion tables, high-precision looks

Between grid points the renderer interpolates — trilinear or tetrahedral interpolation are the usual methods. A 33-point cube with good interpolation is smooth enough for almost every look; conversion tables from camera makers are often 65-point because a Log curve packs a lot of change into its shadows.

Technical LUTs and creative LUTs are different tools

The single most common LUT mistake is treating these two as interchangeable.

• A technical (conversion) LUT maps one encoding to another: Apple Log to Rec.709, S-Log3 to Rec.709, D-Log M to Rec.709. The camera manufacturer publishes it; it has one right answer per camera profile; it is applied first, before any correction.
• A creative LUT expects normal, display-referred video (Rec.709 in practice) and applies a look — a colour palette, a contrast shape, a split tone. It is a matter of taste, and it is applied after exposure and white balance have been corrected.

Apply a creative LUT to un-converted Log and you get a muddy, low-contrast image with wrong skin tones, because the LUT was never designed for that input. Apply a conversion LUT to already-normal footage and you get crushed blacks and blown highlights. The order is not a preference; it is what the tables were built for.

What a LUT cannot do

• Spatial effects. Blur, sharpening, grain, halation and vignettes depend on neighbouring pixels. A LUT sees one pixel at a time.
• Values outside its domain. A .cube is defined from 0 to 1. Anything brighter than the domain is clipped before the table sees it, which is why exposure should be corrected before the LUT, not after.
• Adapting to the shot. A LUT is a fixed mapping. It does not know your white balance was off by 800 K. That is what the adjustment stage between the conversion and the look is for.

Where the .cube format comes from

The .cube format is a plain-text format popularised by IRIDAS and Adobe and now read by nearly every grading tool. A file declares a LUT_3D_SIZE, optionally a DOMAIN_MIN and DOMAIN_MAX, and then lists one output colour per line with the red axis changing fastest. Because it is text, the same file works in DaVinci Resolve, Final Cut Pro, Premiere Pro and LUTLINE. The .cube format guide goes line by line.

How LUTLINE uses LUTs

LUTLINE's recipe has a fixed order because of everything above:

1. Source — the manufacturer's conversion LUT for the detected or chosen camera profile (Apple Log, D-Log M, S-Log3, F-Log, GP-Log, I-Log, L-Log). Standard Rec.709 clips skip it.
2. Adjust — exposure, contrast, white balance and the rest, plus a curve, so the creative LUT receives a corrected image.
3. Look — one of 188 bundled creative LUTs or an imported .cube, blended with the image by an intensity slider (0 % is an exact identity).
4. Finish — an optional finishing LUT for a last technical touch.
5. Film — grain, bloom, halation, dust and RGB split, the spatial effects a LUT cannot produce.

The preview and the export run the same graph, so what the table does on screen is what it does in the file. The step-by-step guide shows the workflow on a real clip.

Frequently asked