An excerpt from the paper
A single objective mottle measurement is described that relates to the full subjective range of visible mottle from “Graininess” to “Patchiness” and multi-color “Wet Trap” to produce a single number ranking mottle within both large and small areas. This new algorithm responds uniformly to all levels of visually apparent mottle in digital images of printed matter and those obtained by opticaltransmission for paper formation measurement. Any digital image of sufficient resolution to visibly display the mottle pattern may be used with the method. When set to do so, it also measures sub-visible mottle found in pitted solid print areas.