Method of measure of roughness of paper based in the analysis of the texture of speckle pattern

Roughness of paper surface is an important parameter in paper manufacturing. Surface roughness measurement is one of the central measurement problems in paper industry. Surfaces are often coated and the amount of coating and method of application used depends on the roughness of the base paper [1], [2]. At the moment, air leak methods are standardized and employed in paper industry as roughness rating methods. Air leak rate between measured paper surface and a specified flat land is recorded by using specialized pneumatic devices under laboratory conditions. Such a measurement closely corresponds to the roughness of a surface, the greater the air leak the rougher the surface. Air leak methods are rather easy to apply to paper and give stable results, although they measure roughness indirectly, need laboratory conditions, and thus unsuitable for on-line use. To measure real topography of paper surface, it is scanned with mechanical or optical profilometers. These methods provide accurate information on surface topography, but also demand laboratory conditions. In our work, present a method of measure based in the analysis of the texture of speckle pattern on the surface. The image formed by speckle in the paper surface is considered as a texture, and therefore texture analysis methods are suitable for the characterization of paper surface. The results are contrasted to air leak methods, optical profilometers (confocal microscopy), and fringe projection.