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Proceedings Paper

Spatial frequency self-filtering and brightness adaption of incoherently illuminated objects
Author(s): Ernst Ulrich Wagemann; Hans J. Tiziani
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Paper Abstract

In this paper an all-optical combination of coherence conversion and spatial frequency self-filtering using two optically addressed liquid crystal (OALC) is presented. A periodic object to be inspected is illuminated by a white light source, imaged onto a OALC and modulates its polarization properties. The OALC then modulates a coherent read-out beam, which can be Fourier transformed to enable frequency self-filtering. Self-filtering uses an additional OALC and is able to detect defects in periodic images. It is independent of the position or rotational orientation of the object and therefore a promising approach for a real-time assembly line inspection. We present experimental results for this cameraless processor and compare it to an alternative approach using a CCD camera and a Matrix-LCD for coherence conversion. In addition adaptive brightness regulation by an OALC in an intermediate image plane is a promising tool for image pre-processing. This adaption process reduces shiny local spots and brightens dark areas. Theory on brightness adaption using an OALC is given and some experimental results are discussed.

Paper Details

Date Published: 9 September 1999
PDF: 10 pages
Proc. SPIE 3823, Laser Metrology and Inspection, (9 September 1999); doi: 10.1117/12.360982
Show Author Affiliations
Ernst Ulrich Wagemann, Univ. Stuttgart (Germany)
Hans J. Tiziani, Univ. Stuttgart (Germany)


Published in SPIE Proceedings Vol. 3823:
Laser Metrology and Inspection
Hans J. Tiziani; Pramod Kumar Rastogi, Editor(s)

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