Page 109 - Graphic Design and Print Production Fundamentals

Graphic Design 97
, and , so our first value is 1.

; and , so our second value is 4.

, so the third value is also 4.

Add them together: ; and take the square root: .

The Delta E (difference) between our two colours is 3. Could we detect that difference if we were
viewing those two colours? Probably just barely. The minimum Delta E for seeing a difference is about
2. Smaller differences can normally be detected in neutral colours (such as our samples), while more
saturated colours require a slightly larger Delta E. A Delta E of 4 is the upper threshold for acceptable
machine repeatability or consistency.

Delta E provides a value indicating the overall difference between two colours. It does not provide any
colour-related data such as which colour is lighter/darker, redder/greener, more blue/more yellow. To
understand how the colours are different, we have to evaluate the comparative L, a, and b differences
independently.

Experimentation over time has come to show that conventional Delta E is about 75% accurate in
showing the difference we see between two colours. Delta E numbers exaggerate the differences in
yellows and compress our perceptual distance between blues. To improve on the representation of our
interpretation of colour difference, scientists have produced a modified formula known as Delta E(94).

Delta E(94)

Delta E(94) is a modified formula that provides about 95% accuracy in correlation to human perception
of colour differences. Here it is in all its splendour:

where:

(for reference conditions)