Using laser speckle to measure the roughness of paper

Paper surface roughness is an important consideration in paper and board destined for printing. The amount of coating and method of application depend on the roughness of the base paper. We present a method to measure the roughness of the paper based on analysis of speckle pattern on the surface. Images are captured by means of a simple configuration using a laser and a charge-coupled device (CCD) camera. Then, we apply digital image processing using a co-occurrence matrix, providing for a noncontact surface profiling method that can be used online.