Delta E
A numerical measure of the perceived difference between two colours, used to quantify display and print accuracy.
Formula / rule
ΔE = distance in CIELAB space
Measured in
ΔE
In depth
A value of 1 is roughly the smallest difference a trained observer can detect under ideal conditions; below 2 is generally considered imperceptible in practice, and above 5 is obvious. It is the standard figure for reporting monitor calibration accuracy and for verifying that a proof matches its reference.
Examples in practice
A display calibrating to an average ΔE of 0.8 is visually indistinguishable from its target across the test patches.