Definition
ΔE(Delta-E, from the Greek δ “difference” and the German Empfindung“sensation”) is the standardised measure for the perceptual difference between two colours. A ΔE of 0 means identical colours; higher values indicate a larger perceived difference.
Background
The first ΔE formula (CIE76) calculated the Euclidean difference in the CIE L*a*b* colour space. Because L*a*b* is not perfectly perceptually uniform, improved formulas followed:
- ΔE*ab (CIE76): simple Euclidean distance
- ΔE*94 (CIE94): corrections for chroma and hue
- ΔE00 (CIEDE2000): full corrections for lightness, chroma, hue and interactions — the current ISO standard (ISO/CIE 11664-6:2014)
Common rules of thumb for CIEDE2000 (industry usage; not a single peer-reviewed source):
| ΔE00 | Interpretation |
|---|---|
| < 0,5 | Not perceptible |
| 0,5 – 1,0 | Barely perceptible (trained eye) |
| 1,0 – 2,0 | Perceptible on direct comparison |
| 2,0 – 5,0 | Clear difference |
| > 5,0 | Large difference — different colour |
Relevance to ColorAptitude™
ColorAptitude™ uses OKLCH-based perceptual distances as the core metric throughout the assessment, including hue ordering, magnitude scaling and threshold modules. CIEDE2000 (ΔE00) is referenced for cross-comparison with industry partners that report deviations in that metric, but it is not the basis of the ColorAptitude scoring pipeline.
OKLCH is more recent (Ottosson, 2020) and offers better hue linearity than CIE L*a*b*, which makes it preferable for digital stimulus generation and for psychophysical scaling — the use cases that underlie ColorAptitude.