Delta E (ΔE)

Delta E (written ΔE or DeltaE) is a numeric measure of the perceptual difference between two colours, computed in a perceptually-uniform colour space (CIELAB, CIE94, CIEDE2000, or modern OKLab). It’s the standard tool for quantifying “how close are these two colours?”

Standard thresholds (using CIEDE2000, the modern reference):

• ΔE < 1: Indistinguishable to most observers.
• 1 < ΔE < 2: Visible on close inspection.
• 2 < ΔE < 4: Visible at a glance.
• 4 < ΔE < 10: Clearly different but related colours.
• ΔE > 10: Different colours.

Where ΔE is used:

• Printing. Pantone matching and print proofing aim for ΔE < 2 between the spec and the printed sheet.
• Display calibration. Professional monitors are sold with ΔE specifications. A “ΔE < 2 out of the box” monitor is accurate enough for photo and design work.
• Colour matching across materials. Paint, plastic, textile, and ink reproductions targeting a master colour.
• Compression and quality. Image codecs (JPEG, WebP, AVIF) optimise to minimise ΔE rather than raw pixel difference.

Several formulas exist for computing ΔE — the older CIE76 (Euclidean distance in CIELAB), the improved CIE94, and the modern CIEDE2000 which corrects perceptual non-uniformities CIE76 missed. For new work use CIEDE2000 unless you specifically need backward compatibility.