Color data parameters
Hunter L, a, b and CIE 1976 L*a*b* (CIELAB) are both color scales based on the Opponent-Color Theory. This theory assumes that the receptors in the human eye perceive color as the following pairs of opposites.
- L scale: Light vs. dark where a low number (0-50) indicates dark and a high number (51-100) indicates light.
- a scale: Red vs. green where a positive number indicates red and a negative number indicates green.
- b scale: Yellow vs. blue where a positive number indicates yellow and a negative number indicates blue.
The L value for each scale therefore indicates the level of light or dark, the a value redness or greenness, and the b value yellowness or blueness. All three values are required to completely describe an object‘s color.
The delta values (∆L, ∆a, and ∆b) indicate how much a standard and sample differ from one another in L, a, and b. The ∆L, ∆a, and ∆b values are often used for quality control or formula adjustment. Tolerances may be set for the delta values. Delta values that are out of tolerance indicate that there is too much difference between the standard and the sample.
The type of correction needed may be determined by which delta value is out of tolerance. For example, if ∆a is out of tolerance, the redness/ greenness needs to be adjusted. Whether the sample is redder or greener than the standard is indicated by the sign of the delta value. For example, if ∆a is positive, the sample is more red than the standard. The total color difference, ∆E, may also be calculated. ∆E is a single value that takes into account the differences between the L, a, and b of the sample and standard. It does not indicate which parameter is out of tolerance if ∆E is out of tolerance. It may also be misleading in some cases where ∆L, ∆a, or ∆b is out of tolerance, but ∆E is still within the tolerance.
Color strength (k/s) value, reflectance (%) and CIE L*a*b* valuefor different substrate can be evaluated in terms of their CIEL*a*b* coordinates and K/S values. The L* (lightness/ darkens), a* (redness/greenness), b* (yellowness/blueness).
The relative color strength (K/S) was calculated using the technique of light reflectance by applying Kubelka-Munk Eqn (Judd and Nickerson, 1975).
