Uwe Dahms

Influence of flatness distortion on the output of a liquid-crystal-television-based joint transform correlator system.

The use of liquid-crystal panels from a commercially available Sanyo video projector as spatial light modulators in a standard joint transform correlator system is investigated. It is found that the flatness distortion of the panels disturbs the output correlation signal in general. Since the reported solutions for the flatness corrections are either expensive (liquid gates) or suffer from low light efficiency (holographic techniques), we have investigated a possibility to minimize the influence of these distortions on the correlation output without flatness correction. First, we quantify optical flatness across the transparent panel area, and then we measure the effects of flatness distortion by changing the display location of the input objects and the resulting joint power spectrum. It is found that the correlation peak is 1 order of magnitude more sensitive to phase distortions of the input scene than to the same distortions of the joint power spectrum. Choosing the flattest location on the panel allows the utilization of the panels to be demonstrated through recognition of cuneiform inscription signs.

Holography and holographic pattern recognition for preservation and evaluation of cultural-historic sources

In the study of ancient cultures, a major difficulty is the fact that available remains of historic and cultural value are often in the possession of different institutions and, therefore, are not directly accessible simultaneously. Even fragments of such objects are often stored at different places, which creates an additional obstacle to the task of their recombination. Moreover, they are endangered by natural or man-made destruction, and many of them are already in such a state, that information regarding the surface structure is hardly interpretable. Thus, techniques for high-resolution 3-D documentation and fine-structure analysis as well as feature enhancement and extraction are indispensable. Documentation by two-dimensional photography gives only a restricted impression of the threedimensional appearance of these objects and is insufficient for a detailed analysis of the spatial fine structure of the surface relief. Plaster casts from molds display the three-dimensional geometry of the object, but show restricted spatial resolution, besides the risk of destruction of fine structures during the molding process. In order to overcome these obstacles holographic techniques can be used because of

Holographic Techniques Application in Analysing Cuneiform Inscriptions

Abstract For the investigation of ancient cuneiform inscriptions, an optoelectronic device with several functions was used and various spatial filtering experiments were performed. By applying twofold amplitude filtering, spatial frequency features of different cuneiform elements have been enhanced, extracted, and analysed. The correlation experiments were performed by applying complex matched filtering. Input data were significantly reduced during the filtering procedures. The results presented demonstrate the possibility of obtaining information such as similarity measures between different objects in the cluttered scene analysis problem.

Characterization of the cuneiform signs by the use of a multifunctional optoelectronic device

The cuneiform-inscription (CI) signs recorded on the original clay tablet known as HS 158b from Nippur (1329 B.C.) have been characterized by the use of a multifunctional optoelectronic device. Properties such as features in object and Fourier space or similarity measures between the CI sign samples were investigated by the application of various numerical and experimental procedures. An overall algorithm of the experimental work is given, and the corresponding particular steps are described. For describing the objects from the CI font numerically, a mathematical model is introduced. To decrease the sensitivity between different samples of a sign (in-class objects) and to increase the discrimination of other signs (out-of-class objects), we designed and implemented, besides digital techniques, a coherent optical technique for averaging a training set of in-class objects. The preliminary correlation experiments conducted on several CI signs illustrate the usefulness of the proposed approach.

Use of a multifunctional extended optical correlator for cuneiform inscription analysis

Ancient cuneiform inscriptions are remains of historic and cultural value. The characterization of cuneiform signs by means of feature enhancement, feature extraction, detection, and identification is therefore of special interest. The use of methods minimizing the in-class objects sensitivity while maximizing the discriminability for out-of-class objects is indispensable due to the inherent sensitivity of optical pattern recognition. To analyze cuneiform inscriptions a multifunctional experimental device was advanced enabling correlation experiments to be performed including an automatic prefiltering procedure. An original technique for coherent optical averaging is introduced. The in-class and out-of-class correlation sensitivities are compared for different types of matched spatial filters including classical single sign filter, optically averaged filter, digitally averaged filter, and multiplexed filter.

Optical pattern recognition in the analysis of ancient Babylonian cuneiform inspection

The subject of interest is ancient Babylonian cuneiform inscriptions in clay tablets representing three-dimensional carriers of information. Investigations have been carried out on original cuneiform signs as well as on models of signs. For the characterization of inscriptions by means of optical pattern recognition techniques an algorithm is presented that includes the following steps: data reduction, feature extraction, average pattern production, power spectrum mask production, average matched spatial filter production, and finally the correlation experiment.

Modulation characteristics of the Sanyo liquid crystal television

The complex transmittance and selected physical parameters of liquid-crystal displays removed from a commercially available Sanyo video projector are studied. The phase modulating behavior and phase and amplitude coupling are determined as function of the video drive signal and the polarizer/analyzer configuration. The suitability of the LC displays as input modulator in a joint transform correlator setup is shown. Correlation experiments with input signals taken from an original Babylonian cuneiform inscription are carried out.

Optische Zeichenerkennung an Keilschriften mit Hilfe holographischer Filterung

Cuneiform inscriptions in clay tablets are historic remainders of one of the first human civilizations on earth. About 500000 of these are stored in different museums all over the world. One aim of historians is to recognize damaged signs and to recombine tablet fragments. For that purpose methods of optical pattern recognition and optoelectronic image processing could be a helpful tool and had to be tested. The application of an extended optoelectronic correlator system to single wedges and models of cuneiform signs is described. The results show that classical matched spatial filters of averaged signs provide low sensitivity for signs that are of the same kind and high-level discrimination capacity for signs not in the same class. D ie Techniken der Holographie werden in vielen Gebieten der optischen Bildverarbeitung zur paralMen Datenverdichtung und Mustererkennung eingesetzt. Bei der Klassifizierung und Dokumentation von arch~ologischen Objekten, insbesondere dreidimensionaler Schrifttrfiger wie Keilschrifttafeln, sowie zu ihrer Archivierung wurden sie bisher jedoch noch nicht verwendet. Anwendungen der Holographie auf diesem Gebiet beschrfinkten sich auf die Gestaltung von Ausstellungen mit Displayhologrammen. Im folgenden soll ein Aspekt der Anwendung holographischer Techniken behandelt werden, der ft~r die LOsung einiger Teilprobleme in der Archfiologie vielversprechende Ansfitze ermOglicht. Archfiologische Fundstt~cke sind der wissenschaftlichen Forschung besonders dann schwer zug~nglich, wenn sie nur in Form von Bruchstt~cken vorliegen, die Oberfl~chen durch Erosion oder Korrosion beeintrfichtigt wurden oder Risse, Kratzer, Verunreinigungen usw. die enthaltenen Informationen nahezu unauswertbar machen. Ft~r die Rekonstruktion von arch~iologischen Fundstacken anhand von Merkmalen, z.B. Konturen und Kanten von Scherben, Strukturierungen auf der Oberffiche sowie Formen, Kr~immungen usw., werden zwar Bildverarbeitungsverfahren angewandt, diese gestatten jedoch lediglich das Zusammenft~gen von Bruchstt~cken, die sich am gleichen Ort befinden [1]. In der Altorientalistik sind hfiufig historische Fundstt~cke, insbesondere Tontafeln mit Keilinschriften bzw. Bruchstt~cke von diesen, an verschiedenen Stellen der Erde gelagert. Sie sind daher nur in wenigen Ffillen der direkten Bearbeitung durch den Epigraphisten zug~nglich. (Eine Einfahrung zu Keilschriften, ihre Struktur und Bedeutung ist zu finden bei Walker [2].) Bei Transporten besteht durch Umwelteinflt~sse, z.B. Feuchtigkeitsfinderungen der Umgebung, die Gefahr, dab die in den Keilschriften enthaltenen Informationen, die Zeugnis aber mehrere Jahrtausende Menschheitsgeschichte ablegen, zerstOrt werden und damit far immer verlorengehen.

Optimization steps in a cuneiform inscription characterization process

Recently, an investigation of using holographically based techniques for the cuneiform inscription characterization has been reported in several publications. This paper provides an overview of the development of the experimental systems and techniques. Particularly, we describe the main optimization steps as well as the selected correlation results, and the general frame of the future work.

Complex transmittance of the Sanyo liquid crystal television: experimental and theoretical investigations

The complex transmittance and selected physical parameters (molecular director, twist angle, optical flatness, static intensity contrast ratio) of liquid-crystal displays removed from a commercially available Sanyo video projector are studied. The phase modulating behavior and phase and amplitude coupling are determined as function of the video drive signal and the polarizer/analyzer configuration. The suitability of the LC displays as input modulator in a joint transform correlator (JTC) setup is shown. Correlation experiments with input signals taken from an original Babylonian cuneiform inscription are carried out. The influence of small rotations of the target sign as well as small changes in size of the target on the correlation spot height is studied.