The Just Noticeable Difference is a psychophysical concept defining the smallest change in a stimulus (here, color) that a human observer can detect. In color science, it provides the practical threshold below which two colors are effectively indistinguishable.
Delta E (ΔE) and the JND
The CIELAB Delta E (ΔE) metric was designed so that a value of 1.0 roughly corresponds to one JND under controlled laboratory conditions. In practice, the thresholds are commonly interpreted as:
- ΔE < 1.0 — Not perceptible to most people
- ΔE 1–2 — Perceptible through close observation
- ΔE 2–10 — Perceptible at a glance
- ΔE > 10 — Obviously different colors
Practical Application: Color Grouping Thresholds
Our palette extraction uses a grouping threshold of 32 in RGB Euclidean distance. This is deliberately much larger than the JND because the goal is to merge visually similar colors, not identify barely-distinguishable ones. A JND-based threshold would produce a palette with too many entries to be useful.
However, JND is critical for quality control: if a printed reproduction has a ΔE of less than 1.0 compared to the original, the colors are considered a perfect match.