How do I know if a LUT is accurate?

Apply the LUT to a ColorChecker chart and inspect the result. The neutral grey patches should stay neutral (equal R, G, and B — no colour cast), and known colours like skin tones and primaries should land close to their reference values. For an objective answer, measure the CIEDE2000 ΔE of each patch against the reference: under 2 is excellent, 2–5 is acceptable, above 5 is a visible shift.

Do I need a physical ColorChecker to test a LUT?

No. To test a LUT you're testing the transform, not a real scene, so a digital ColorChecker generated from the official Lab reference values works — and it's more precise because there's no lens, lighting, or JPEG compression involved. A physical chart is only needed when you have to photograph it under real light.

What ΔE is acceptable for a LUT?

For a technical or corrective LUT that's meant to be accurate, aim for an average ΔE2000 under 2 and no single patch far above 5. Creative looks intentionally shift colour, so ΔE isn't the right measure for them — there you're judging intent, not accuracy.

July 3, 2026·dom @ luttie

How to Verify a LUT Is Color-Accurate (Step by Step)

A practical way to test whether a LUT is accurate: run a ColorChecker through it and measure the ΔE. Here's the full workflow, what to look for, and how to read the numbers — no expensive gear.

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A LUT is a black box: it maps input colours to output colours, but the file itself tells you nothing about how it behaves. Before you trust a LUT on real footage — especially a technical or corrective one — it's worth verifying it. Here's a repeatable way to do that without expensive gear.

Why verify a LUT at all?

There are two kinds of LUT. A creative LUT is supposed to shift colour — that's the look. A technical LUT (a log-to-Rec709 transform, a camera-matching LUT, a corrective grade) is supposed to be accurate. The problem is that both arrive as the same kind of .cube file, and a technical LUT that quietly introduces a green cast or crushes your shadows will ruin footage in ways you won't notice until it's too late.

Verifying takes about a minute and turns "looks fine, I think" into a number.

The tool: a ColorChecker chart

The standard reference is the 24-patch ColorChecker — natural colours (skin, sky, foliage), saturated primaries, and a neutral grey ramp, each with a precisely defined value. You don't need the $80 physical chart to test a LUT: grab the free digital ColorChecker, which is generated from the official X-Rite Lab D50 reference values. (More on when digital is enough vs. a physical chart.)

Step by step

Open the chart in your grading tool — or drop it straight into the Luttie editor.
Apply the LUT you want to test.
Check the neutral row first. The six grey patches along the bottom should stay perfectly neutral — equal red, green, and blue. Any tint here means the LUT has a colour cast, and a cast in the greys will show up everywhere.
Check the greyscale range. The white patch shouldn't be blown out; the black shouldn't be crushed. If detail is gone at either end, the LUT is clipping.
Check skin and primaries. Skin-tone patches should look natural, not orange or magenta. Reds should read red, not orange; blues blue, not purple.

Turn it into a number: measure ΔE

Eyeballing catches gross errors, but "does the grey look neutral?" is subjective. To make it objective, measure the ΔE — the perceptual colour difference between each measured patch and its reference value. The modern formula is CIEDE2000.

The quickest way: export your graded chart and run it through the free color accuracy checker. It samples all 24 patches and reports the ΔE of each against the X-Rite reference.

How to read the result:

ΔE < 1 — imperceptible
ΔE < 2 — excellent; the LUT is accurate
ΔE 2–5 — acceptable for most work
ΔE > 5 — a visible shift you can see by eye

For a technical LUT, aim for an average ΔE2000 under 2 with no single patch stranded far above 5. If the greys are clean but a couple of saturated primaries are high, that's usually fine — saturated colours are the hardest to hit and matter less than neutrals for most footage.

A note on creative looks

Don't run this test on a creative LUT and panic at a ΔE of 12. A film-emulation or teal-and-orange look is meant to move colour a long way from neutral — a high ΔE there is the point, not a bug. Accuracy testing is for LUTs that claim to be faithful. For creative looks, judge intent, not distance from a reference.

Do it once, trust it forever

Verifying a LUT is a one-time, one-minute check that pays for itself the first time it catches a cast before you've graded a whole project on top of it. Grab the ColorChecker, run it through the accuracy checker, and you'll know exactly what any LUT is doing to your colour.