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Auflistung nach Autor:in "Riess, Christian"

1 - 4 von 4
  • Konferenzbeitrag
    The spectral relation between the cube-connected cycles and the shuffle-exchange network
    (ARCS 2012 Workshops, 2012) Riess, Christian; Strehl, Volker; Wanka, Rolf
    We investigate the relation between the spectral sets (i. e., the sets of eigenvalues, disregarding multiplicities) of two d-dimensional networks popular in parallel computing: the Cube-Connected Cycles network CCC(d) and the Shuffle-Exchange network SE(d). We completely characterize their spectral sets. Additionally, it turns out that for any odd d, the SE(d)-eigenvalues set is precisely the same as the CCC(d)- eigenvalues set. For any even d, however, the SE(d)-eigenvalues form a proper subset of the set of CCC(d)-eigenvalues.
  • Zeitschriftenartikel
    The Spectral Relation between the Cube-Connected Cycles and the Shuffle-Exchange Network
    (PARS: Parallel-Algorithmen, -Rechnerstrukturen und -Systemsoftware: Vol. 29, No. 1, 2012) Riess, Christian; Strehl, Volker; Wanka, Rolf
    We investigate the relation between the spectral sets (i. e., the sets of eigenvalues, disregarding multiplicities) of two d-dimensional networks popular in parallel computing: the Cube-Connected Cycles network CCC(d) and the Shuffle-Exchange network SE(d). We completely characterize their spectral sets. Additionally, it turns out that for any odd d, the SE(d)-eigenvalues set is precisely the same as the CCC(d)eigenvalues set. For any even d, however, the SE(d)-eigenvalues form a proper subset of the set of CCC(d)-eigenvalues.
  • Konferenzbeitrag
    A study on features for the detection of copy-move forgeries
    (Sicherheit 2010. Sicherheit, Schutz und Zuverlässigkeit, 2010) Christlein, Vincent; Riess, Christian; Angelopoulou, Elli
    Blind image forensics aims to assess image authenticity. One of the most popular families of methods from this category is the detection of copy-move forgeries. In the past years, more than 15 different algorithms have been proposed for copy-move forgery detection. So far, the efficacy of these approaches has barely been examined. In this paper, we: a) present a common pipeline for copy-move forgery detection, b) perform a comparative study on 10 proposed copy-move features and c) introduce a new benchmark database for copy-move forgery detection. Experiments show that the recently proposed Fourier-Mellin features perform outstandingly if no geometric transformations are applied to the copied region. Furthermore, our experiments strongly support the use of kd-trees for the matching of similar blocks instead of lexicographic sorting.
  • Konferenzbeitrag
    Towards Forensic Exploitation of 3-D Lighting Environments in Practice
    (SICHERHEIT 2018, 2018) Seuffert, Julian; Stamminger, Marc; Riess, Christian
    The goal of image forensics is to determine authenticity and origin of a digital image or video without an embedded security scheme. Among the existing methods, the probably most well-known physics-based approach is to validate the distribution of incident light on objects of interest. Inconsistent lighting environments are considered as an indication of image splicing. However, one drawback of this approach is that it is quite challenging to use it in practice. In this work, we propose several practical improvements to this approach. First, we propose a new way of comparing lighting environments. Second, we present a factorization of the overall error into its individual contributions, which shows that the biggest error source are incorrect geometric fits. Third, we propose a confidence score that is trained from the results of an actual implementation. The confidence score allows to define an implementation- and problem-specific threshold for the consistency of two lighting environments.