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Interpolation Record

Guide

The interpolation record

Every look here is baked into a 33 × 33 × 33 colour table and read with trilinear interpolation. We measured whether the fancier tetrahedral method would make a visible difference. It would not, so we publish the numbers and keep the simpler one.

What was measured

A colour table stores the answer for a grid of input colours and works out everything in between. Trilinear interpolation blends the eight grid points around a colour; tetrahedral splits that little cube into six pyramids and blends only four, which follows the neutral axis more faithfully and is what many colour-grading programs use. The question is whether that matters for this site’s looks.

On 2026-10-31, a script in this site’s repository (scripts/accuracy-record.mjs) ran all 56 looks over 311 fixed colours — a 33-step grey ramp, skin, sky and foliage patches, the primaries and secondaries, and 256 seeded random colours — at three table sizes, read both ways from 8-bit tables, as the graphics card stores them. Each answer was compared with the exact recipe maths using ΔE00, where about 1.0 is the smallest difference most people can see side by side.

The result

TableTrilinear: mean / worst ΔE00Tetrahedral: mean / worst ΔE00
17³0.11 / 1.860.13 / 2.74
33³ (used)0.10 / 0.900.11 / 0.90
65³0.10 / 0.900.11 / 0.90

At the 33-point size this site uses, the average error is about a tenth of a just-noticeable difference either way, and the worst single colour across every look stays under 1.0. Tetrahedral beat trilinear by half a unit or more on 0 of 56 looks. That is a null result, and it is published as one: the decision recorded by the script is trilinear.

The looks with the largest worst-case error at 33³:

LookTrilinear 33³ mean / worstTetrahedral 33³ mean / worst
Dark Academia0.10 / 0.900.11 / 0.90
Bleach Bypass0.11 / 0.900.12 / 0.90
Slide Fifty0.08 / 0.830.09 / 0.83
Warm Portrait0.11 / 0.820.12 / 0.82
Everyday Negative0.11 / 0.810.11 / 0.81
Faded Print0.10 / 0.780.12 / 0.78
Milk Tea0.11 / 0.770.12 / 0.77
Y2K Cyan0.09 / 0.770.09 / 0.77

Why the bigger table does not help either

Going from 33 to 65 points barely moves the numbers, because what is left is mostly the 8-bit rounding of the stored table, not the interpolation. The 17-point table is where the shape of the grid starts to show, and there trilinear is the better of the two. A .cube you import is read the same way, at whatever size it was written.

  • This measures the colour table against the recipe maths in floating point. It does not measure your screen or the graphics card's own interpolation precision.
  • Effects (grain, vignette, glow, halation, the date stamp) are not in the table and are not part of this record.
  • An imported .cube is measured by whoever made it; this record covers this site's own looks.

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