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Today, typical polymer films consist of several functional layers, like printable surface or barrier layers. They are produced in coextrusion processes, in which the different materials are extruded through a single die and formed to a blown-or cast film with haul-off speeds up to 500 m/min. In the production of transparent multilayer films certain defects, called "interfacial instabilities", can occur. They emerge from shear stress and turbulences in the material flow during the process and result in a reduction of the mechanical properties and the optical quality of the product. Interfacial instabilities cannot be detected by conventional film inspection systems available on the market because the optical distortions they produce do not change the brightness of a pixel.In this paper, an approach for solving this problem is presented. The film is illuminated with a patterned line-light source in a backlight setting and a CCD line scan camera is used for recording the image lines. The defects can be detected using a 1D filter tuned to the spatial-frequency of the pattern. The distortion caused by the defects leads to a local extremum in the feature image generated by the filter, which can be easily detected by threshold segmentation.The system has been tested in an industrial setting and proved to be fast enough for inline-inspection. Further applications could be in the fast deflectometric inspection of high-gloss surfaces.

Bedruckte oder geprägte Kunststoffoberflächen sind insbesondere in der Möbel- und Autoindustrie beliebte Dekorelemente. Mit den verfügbaren Bildverarbeitungssystemen ist nur die Inspektion unstrukturierter Folien möglich. Bei unregelmäßigen Texturen, wie zum Beispiel Kunstleder oder Holzimitat, können diese Systeme die Fehlstellen nicht von der gewünschten Textur unterscheiden. Durch die Verwendung von Texturanalysealgorithmen wird auch für diese Produkte eine durchgängige Qualitätskontrolle möglich. Die Fehlstellen können in Echtzeit detektiert und klassifiziert werden.

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