CMC dE represents a color difference value calculated using the CMC l:c formula, a color difference equation developed for improved perceptual uniformity.
CMC dE, often denoted as ΔE_CMC, refers to the numerical measure of color difference between two samples as calculated by the CMC l:c formula. This method was specifically designed to address limitations found in earlier color difference formulas, aiming for results that correlate better with human visual perception, especially in specific industries.
Origin of the CMC l:c Formula
The CMC l:c color difference method was developed by the Colour Measurement Committee of the Society of Dyers and Colourists (CMC).
As per the reference: "The Colour Measurement Committee of the Society of Dyers and Colourists (CMC) defined a new color difference method in 1984, named after the developing committee, CMC l:c."
Introduced in 1984, this formula was one of the first attempts to improve upon the CIE 1976 L*a*b* (CIELAB) color difference formula (ΔE*ab) by incorporating weighting factors that better reflect how humans perceive differences in lightness, chroma, and hue.
Understanding the CMC l:c Components
The "l:c" in the name refers to the two primary weighting factors used in the calculation:
- l (Lightness): This factor weights the contribution of lightness differences (L*) to the overall color difference.
- c (Chroma/Hue): This factor weights the contribution of chroma (C*) and hue (h*) differences.
These weighting factors are adjustable, allowing the formula to be tailored for different applications and viewing conditions. The ratio of l to c determines the relative importance placed on lightness versus chroma/hue differences.
Common l:c Ratios
Different industries or applications often use specific standard l:c ratios:
- 2:1: Commonly used in the textile industry. This ratio gives twice as much weight to lightness differences compared to chroma and hue differences, reflecting the higher visual sensitivity to lightness variations in textiles.
- 1:1: Used in some other applications where lightness, chroma, and hue differences are considered equally important.
Why Use CMC dE?
The primary advantage of using the CMC l:c formula is its improved correlation with visual assessment compared to the simpler ΔE*ab formula. It provides a more perceptually uniform color space around a given standard, meaning that a CMC dE value of 1.0 represents approximately the same perceived color difference regardless of the color's position in the color space.
- Better Agreement: Results align more closely with how people actually see and judge color differences.
- Industry Standard: Widely adopted in industries like textiles, where accurate color matching is critical.
- Tolerance Setting: Makes setting practical color tolerances easier and more reliable.
In summary, CMC dE is the quantified color difference using a specific, perceptually refined formula developed by the CMC committee in 1984, notable for its adjustable weighting of lightness versus chroma/hue differences.
