DeltaE94

DeltaE94 is a color-difference metric introduced in 1994 by Sharma, Wu, and Dalal as an improvement over the CIELAB-based DeltaE76. It was developed to address perceptual nonuniformities in human color vision that DeltaE76 could exaggerate or understate in certain regions of color space. DeltaE94 remains a reference point in discussions of color difference metrics and is still encountered in historical data, printing, and textile contexts.

The method operates on the CIE Lab color space. For two colors with coordinates (L1, a1, b1) and (L2, a2, b2), compute L-difference ΔL = L2 − L1 and chroma values C1 = sqrt(a1^2 + b1^2), C2 = sqrt(a2^2 + b2^2), with ΔC = C2 − C1. Define ΔEab^2 = ΔL^2 + Δa^2 + Δb^2 and ΔH' = sqrt( ΔEab^2 − ΔL^2 − ΔC^2 ), where ΔH' represents the hue difference component. The final DeltaE94 value is

ΔE94 = sqrt( (ΔL / (kL S_L))^2 + (ΔC / (kC S_C))^2 + (ΔH' / (kH S_H))^2 ),

where kL, kC, kH are perceptual weighting factors (often set to 1) and S_L, S_C, S_H are weighting functions that adjust sensitivity to lightness, chroma, and hue. Common defaults are S_L = 1, S_C = 1 + 0.045 C1, S_H = 1 + 0.015 C1, with C1 being the chroma of the first color. In practice, kL, kC, kH may be tuned for specific viewing conditions, and there are industry-specific parameterizations (e.g., for graphic arts or textiles).

DeltaE94 has largely been superseded by DeltaE2000 (CIEDE2000) for higher perceptual accuracy, but it remains encountered in legacy datasets and certain quality-control workflows.