sentences:  It is assumed that the revealing layer is printed on a transparency and is superimposed on top of the base layer, which can be printed either on a transparency or on an opaque paper.The periods of the two layer patterns are close.We denote the period of the base layer as "p"b and the period of the revealing layer as "p"r.
  
  The superposition image of Figure 1 outlines periodically repeating dark parallel bands, called moiré lines.