Measure perceptual color distance
Name the color-difference formula whenever the numeric result drives a decision.
CIEDE2000
2.04246
DeltaE94
6.02425
CMC 2:1
1.73874
The number depends on the algorithm
The same Lab pair produces materially different values under CIEDE2000, DeltaE94, and CMC 2:1. Store the algorithm beside the result.
Select the formula explicitly
Color::distance() defaults to CIEDE2000. Pass a supported algorithm name when your tolerance or domain requires another formula.
<?php
use PhpColor\Color\Color;
use PhpColor\Color\LabColor;
$a = new LabColor(50.0, 2.6772, -79.7751);
$b = new LabColor(50.0, 0.0, -82.7485);
printf("CIEDE2000 %.13f\n", Color::distance($a, $b));
printf("DeltaE94 %.13f\n", Color::distance($a, $b, 'DeltaE94'));
printf("CMC %.13f\n", Color::distance($a, $b, 'CMC'));
// CIEDE2000 2.0424596801566
// DeltaE94 6.0242477679966
// CMC 1.7387361057262A distance needs a policy
The method returns a measurement, not an automatic acceptable or unacceptable verdict. Define thresholds for the material and task you are evaluating.
CIEDE2000The default general Lab color-difference formula.
DeltaE94A different formula with its own weighting model.
CMCThe default CMC alias uses the 2:1 acceptability parameters.
AlphaThese Lab distance calculations do not evaluate backdrop-dependent transparency.