Gloss Mottle Measurement: Black, Dark Printed Areas, and Wet Trap

It is possible to measure the degree of mottle present in very low contrast full color digital images. Under normal illumination these prints may not display any visual evidence of mottle unless viewed in low incident angle light. Typically these images are from four color black offset print (400% black), dark offset wet trap colors and dark print areas using other printing techniques. The methods employed and the results of tests used in the measurement are presented. In order to encourage the adoption of an international standard for the measurement of mottle in general, the image analysis techniques and methods used to extract the mottle patterns and the equations used in the measurement algorithms are disclosed.