Method for monitoring multiple water marks that are utilized as safety features in structure of papers for producing e.g. bank notes, involves outputting signal, when number of image points of image is greater than value

摘要

The method involves defining a threshold value, and determining number of image points of a difference image whose gray level is smaller than the threshold value. The difference image is determined from a water mark area and smoothened image of water mark regions. Another threshold value is defined, and the determined number of points of the image is compared with the latter value. Two signals are output, when the determined number of points of the image is smaller and greater than the latter value, respectively.