12 September 2014 Near-field imaging techniques for surface inspection
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Following the recent work on the characterization of flexo-printing plates a concept for inspection of glossy surfaces using a defined out of focus image of the surface under parallel illumination is presented, which in principle represents a near field distribution of the reflection function of the surface. The image turns out to be equivalent to a focussed shadowgraph as used for the investigation of processes in transparent media. Beside the plain ’reflected shadow imaging’ several degrees of freedom can be exploited for configuration of the feature emphasis. The method is especially interesting for the quality control of printed matter. In the paper the definition of the system, the mechanism of the imaging process and its relation to the real image of the surface itself are considered. Further, questions of resolution, extractable features and extended applications are discussed.
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Florian Dannenberg, Cornelius Hahlweg, Lukas Pescoller, Wenjing Zhao, "Near-field imaging techniques for surface inspection", Proc. SPIE 9193, Novel Optical Systems Design and Optimization XVII, 91930Q (12 September 2014); doi: 10.1117/12.2062316; https://doi.org/10.1117/12.2062316

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