The opacity of paper can affect its color. For single-sheet measurements in particular, a change in opacity results in a change in color. When taking color measurements in a laboratory using a benchtop instrument, a “stack” is created by folding the paper a number of times until it appears opaque. However, an on-line instrument viewing paper as it is manufactured can only measure a single thickness
of paper as it passes under the sensor, so the color values may be different than those obtained from a benchtop instrument because the opacity is different.
HunterLab has developed hardware and software options that together compensate for these differences in opacity. The hardware moves an everwhite backing tile underneath the paper and then away from the paper. The software calculates color corrected for opacity using the formulas shown below, based on the Kubelka-Monk algorithm.
(See attached pdf file for the complete article and formulas)