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13 June 2005 3D measurement of human face by stereophotogrammetry
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At present several methods are adapted for the optical characterization of 3D surface profiles and forms, which are based on fringe projection, moire techniques, gray-code projection or photogrammetry [1-5]. According to principle and application the methods differ in accuracy of measurement as well as computation time or their technical complexity. Photogrammetry is a well-adapted method for the measurement of 3D objects. The basic idea of the method is to get the whole 3D matrix of real objects by capturing a number of 2D images. In this work we show a possibility for a rapid measurement (< 1 second) of the shape of a human face for medical applications (e. g. jaw-measurement). The surface structure of the human face is too homogenous to find homologous points by an ordinary illumination; therefore about 20 special statistical patterns are projected on the face and taken by cameras of a convergent stereo system. At present a digital projector is used but it is also possible to generate the statistical patterns by a classical one. To find the corresponding points in the pictures we use an enhanced correlation technique, which takes into account the characteristic intensity sequence of every single sensor element - unlike other correlation techniques, which avail a pixel area as a template. The influence of distortion - caused by the surface profile - is kept to a minimum. Therefore at higher profile gradients a denser point cloud is generated. At present the reachable accuracy is +/- 0.1mm (rms), which is sufficient for medical and other applications. But the demonstrated method is not restricted to evaluate the shape of human faces. Also technical objects could be measured.
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Holger Wagner, Axel Wiegmann, Richard Kowarschik, and Friedrich Zollner "3D measurement of human face by stereophotogrammetry", Proc. SPIE 5856, Optical Measurement Systems for Industrial Inspection IV, (13 June 2005);

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