Browsing by Author "Brenner, Simon"

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    An Investigation of Optimal Light Source Setups for Photometric Stereo Reconstruction of Historical Coins
    (The Eurographics Association, 2018) Brenner, Simon; Zambanini, Sebastian; Sablatnig, Robert; Sablatnig, Robert and Wimmer, Michael
    In this paper, we address the 3D reconstruction of historical coins by means of Photometric Stereo. We investigate the influence of the number and arrangement of lights to the reconstruction quality by comparing mean angular errors on 22 historical coin models. Our results demonstrate that 6 lights circularly placed at an optimal elevation angle do not show a significant loss of reconstruction quality compared to a full semispherical dome setup with 54 lights. This represents a considerable saving of acquisition time and system complexity when it comes to the mass digitization of historical coins.
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    Lens Calibration for Focus Shift Correction in Close-Range Multispectral Imaging
    (The Eurographics Association, 2019) Brenner, Simon; Sablatnig, Robert; Rizvic, Selma and Rodriguez Echavarria, Karina
    Multispectral imaging has become a popular tool to reveal properties and structures in cultural heritage objects that are hidden to the human observer. One of the inherent problems of multispectral imaging applications is chromatic aberration. Due to an extended spectral range, the effect appears more pronounced than in conventional photography in the visible spectrum. This paper is concerned with longitudinal chromatic aberrations, i.e. shifts of the focal plane along the principal axis of the camera, as they are hard to correct in post-processing and should be avoided during acquisition. To this end, a calibration scheme to measure the wavelength- and distance-dependent focal shift behavior of a given camera/lens system is proposed, which allows for a mechanical compensation at acquisition time. The approach is demonstrated on a multispectral imaging system for historical manuscript analysis. We show that the application of this compensation approach enables the acquisition of in-focus images in non-visible wavelengths using a lens optimized for the visible spectrum only.