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DeltaE94 has largely been superseded by DeltaE2000 (CIEDE2000) for higher perceptual accuracy, but it remains encountered in legacy datasets and certain quality-control workflows.