DeltaEab

DeltaEab, often written as DeltaE*ab or ΔEab, is a scalar metric used to quantify the difference between two colors in the CIELAB color space. It is defined as the Euclidean distance between the two colors’ L*a*b* coordinates: ΔEab = sqrt((L2* − L1*)^2 + (a2* − a1*)^2 + (b2* − b1*)^2). In this space, L* represents lightness (0 is black, 100 is white), a* encodes red–green, and b* encodes yellow–blue. The metric provides a single numeric value that approximates perceptual color difference for many practical applications, such as quality control and color matching.

Origin and variants form part of its history. The ΔE*ab metric originated with the CIELAB color space defined by the CIE in 1976. It was found to be not perfectly perceptually uniform, prompting later refinements such as ΔE*94 (CIE94) and ΔE*2000 (CIEDE2000), which apply weighting factors and nonuniformity corrections to better align differences with human vision. The term ΔEab is sometimes used to refer to the original ΔE*ab, but modern practice often relies on perceptual difference formulas like CIEDE2000 for higher accuracy.

Usage and limitations are important for interpretation. DeltaE is widely used in printing, manufacturing, graphic arts, and color science to determine whether color differences fall within acceptable tolerances. However, because Lab is not perfectly perceptually uniform under all conditions, ΔE values can be misleading across different colors, illuminants, or viewing environments. Color management systems and perceptual difference formulas such as CIEDE2000 are often employed to improve decision criteria.