Browsing by Author "Onural, L."
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Item Open Access 3-D motion estimation and wireframe adaptation including photometric effects for model-based coding of facial image sequences(IEEE, 1994-06) Bozdağı, G.; Tekalp, A. M.; Onural, L.We propose a novel formulation where 3-D global and local motion estimation and the adaptation of a generic wireframe model to a particular speaker are considered simultaneously within an optical flow based framework including the photometric effects of the motion. We use a flexible wireframe model whose local structure is characterized by the normal vectors of the patches which are related to the coordinates of the nodes. Geometrical constraints that describe the propagation of the movement of the nodes are introduced, which are then efficiently utilized to reduce the number of independent structure parameters. A stochastic relaxation algorithm has been used to determine optimum global motion estimates and the parameters describing the structure of the wireframe model. Results with both simulated and real facial image sequences are provided.Item Open Access 3-D motion estimation of rigid objects for video coding applications using an improved iterative version of the E-matrix method(Institute of Electrical and Electronics Engineers, 1998-02) Alatan, A. A.; Onural, L.As an alternative to current two-dimensional (2-D) motion models, a robust three-dimensional (3-D) motion estimation method is proposed to be utilized in object-based video coding applications. Since the popular E-matrix method is well known for its susceptibility to input errors, a performance indicator, which tests the validity of the estimated 3-D motion parameters both explicitly and implicitly, is defined. This indicator is utilized within the RANSAC method to obtain a robust set of 2-D motion correspondences which leads to better 3-D motion parameters for each object. The experimental results support the superiority of the proposed method over direct application of the E-matrix method.Item Open Access 3D model compression using connectivity-guided adaptive wavelet transform built into 2D SPIHT(Academic Press, 2010-01) Köse K.; Çetin, A. Enis; Güdükbay, Uğur; Onural, L.Connectivity-Guided Adaptive Wavelet Transform based mesh compression framework is proposed. The transformation uses the connectivity information of the 3D model to exploit the inter-pixel correlations. Orthographic projection is used for converting the 3D mesh into a 2D image-like representation. The proposed conversion method does not change the connectivity among the vertices of the 3D model. There is a correlation between the pixels of the composed image due to the connectivity of the 3D mesh. The proposed wavelet transform uses an adaptive predictor that exploits the connectivity information of the 3D model. Known image compression tools cannot take advantage of the correlations between the samples. The wavelet transformed data is then encoded using a zero-tree wavelet based method. Since the encoder creates a hierarchical bitstream, the proposed technique is a progressive mesh compression technique. Experimental results show that the proposed method has a better rate distortion performance than MPEG-3DGC/MPEG-4 mesh coder.Item Open Access 3DTV: Capture, transmission, and Display of 3D Video(2009) Triantafyllidis, G. A.; Çetin, A. Enis; Smolic, A.; Onural, L.; Sikora, T.; Watson, J.[No abstract available]Item Open Access A aurvey of signal processing problems and tools in holographic three-dimensional television(Institute of Electrical and Electronics Engineers, 2007) Onural, L.; Gotchev, A.; Özaktaş, Haldun M.; Stoykova, E.Diffraction and holography are fertile areas for application of signal theory and processing. Recent work on 3DTV displays has posed particularly challenging signal processing problems. Various procedures to compute Rayleigh-Sommerfeld, Fresnel and Fraunhofer diffraction exist in the literature. Diffraction between parallel planes and tilted planes can be efficiently computed. Discretization and quantization of diffraction fields yield interesting theoretical and practical results, and allow efficient schemes compared to commonly used Nyquist sampling. The literature on computer-generated holography provides a good resource for holographic 3DTV related issues. Fast algorithms to compute Fourier, Walsh-Hadamard, fractional Fourier, linear canonical, Fresnel, and wavelet transforms, as well as optimization-based techniques such as best orthogonal basis, matching pursuit, basis pursuit etc., are especially relevant signal processing techniques for wave propagation, diffraction, holography, and related problems. Atomic decompositions, multiresolution techniques, Gabor functions, and Wigner distributions are among the signal processing techniques which have or may be applied to problems in optics. Research aimed at solving such problems at the intersection of wave optics and signal processing promises not only to facilitate the development of 3DTV systems, but also to contribute to fundamental advances in optics and signal processing theory.Item Open Access Calculation of the scalar diffraction field from curved surfaces by decomposing the three-dimensional field into a sum of Gaussian beams(Optical Society of America, 2013) Şahin, E.; Onural, L.We present a local Gaussian beam decomposition method for calculating the scalar diffraction field due to a twodimensional field specified on a curved surface. We write the three-dimensional field as a sum of Gaussian beams that propagate toward different directions and whose waist positions are taken at discrete points on the curved surface. The discrete positions of the beam waists are obtained by sampling the curved surface such that transversal components of the positions form a regular grid. The modulated Gaussian window functions corresponding to Gaussian beams are placed on the transversal planes that pass through the discrete beam-waist position. The coefficients of the Gaussian beams are found by solving the linear system of equations where the columns of the system matrix represent the field patterns that the Gaussian beams produce on the given curved surface. As a result of using local beams in the expansion, we end up with sparse system matrices. The sparsity of the system matrices provides important advantages in terms of computational complexity and memory allocation while solving the system of linear equations.Item Open Access Circular holographic video display system(Optical Society of American (OSA), 2011) Yaraş, F.; Kang, H.; Onural, L.A circular holographic video display system reconstructs holographic video. Phase-only spatial light modulators are tiled in a circular configuration in order to increase the field of view. A beam-splitter is used to align the active area of the SLMs side by side without any gap. With the help of this configuration observers can see 3D ghost-like image floating in space and can move and rotate around the object. The 3D reconstructions can be observed binocularly. Experimental results are satisfactory. © 2011 Optical Society of America.Item Open Access A class of adaptive directional image smoothing filters(Elsevier BV, 1996-12) Gürelli, M. İ.; Onural, L.The gray level distribution around a pixel of an image usually tends to be more coherent in some directions compared to other directions. The idea of adaptive directional filtering is to estimate the direction of higher coherence around each pixel location and then to employ a window which approximates a line segment in that direction. Hence, the details of the image may be preserved while maintaining a satisfactory level of noise suppression performance. In this paper we describe a class of adaptive directional image smoothing filters based on generalized Gaussian distributions. We propose a measure of spread for the pixel values based on the maximum likelihood estimate of a scale parameter involved in the generalized Gaussian distribution. Several experimental results indicate a significant improvement compared to some standard filters.Item Open Access A comparative study of light field representation and integral imaging(Taylor and Francis, 2013-07-18) Sahin, E.; Onural, L.Light field representation is a model for three-dimensional (3D) image representation and integral imaging is an optical 3D imaging and representation method. A comparative investigation of light field representation and integral imaging is given in this paper. The practical integral imaging is shown to be equivalent to the discrete light field representation if some restrictions are imposed on the light field. On the other hand, it is shown that the integral imaging is not equivalent to the continuous light field representation. In any case, physical realisation of an arbitrary abstract light field representation may not be possible due to restrictions associated with the uncertainty principle related to the spatial and angular resolutions.Item Open Access Convolution, filtering, and multiplexing in fractional Fourier domains and their relation to chirp and wavelet transforms(1994) Özaktaş, Haldun M.; Barshan, B.; Mendlovic, D.; Onural, L.A concise introduction to the concept of fractional Fourier transforms is followed by a discussion of their relation to chirp and wavelet transforms. The notion of fractional Fourier domains is developed in conjunction with the Wigner distribution of a signal. Convolution, filtering, and multiplexing of signals in fractional domains are discussed, revealing that under certain conditions one can improve on the special cases of these operations in the conventional space and frequency domains. Because of the ease of performing the fractional Fourier transform optically, these operations are relevant for optical information processing.Item Open Access Design and implementation of a general-purpose median filter unit in CMOS VLSI(IEEE Solid-State Circuits Society, 1990) Karaman, M.; Onural, L.; Atalar, AbdullahA general-purpose median filter unit configuration is proposed in the form of two single-chip median filters, one extensible and one real-time. The networks of the chips are pipelined and systolic at bit level and based on the odd/even transposition sorting. The chips are implemented in 3-μm standard CMOS by using full-custom VLSI design techniques. The exact median of elements, in a window size w = 9 with arbitrary word length L, can be found by using only one extensible median filter chip. The filter can be extended to arbitrary window size and word lengths by using many chips. For w > 9 with arbitrary L, the number of chips required to find the exact medians is no more than the smallest greater integer of (w/9)2. Simulation results show that the extensible median filter chip can be clocked up to 40 MHz, and generate 30/L megamedians per second. On the other hand, the real-time median filter chip can find the exact running medians of elements in a window of a fixed size w = 9 with L = 8. According to simulations, it can generate up to 50 megamedians per second with a 50-MHz clock. The chips can be used for the realization of various median filtering techniques. In this paper, the algorithms, VLSI implementations, and testing of the chips are presented together with some possible applications. 0018-9200/90/0400-0505$01.00 © 1990 IEEEItem Open Access Diffraction field computation from arbitrarily distributed data points in space(Elsevier BV, 2007-02) Esmer, G. B.; Uzunov, V.; Onural, L.; Özaktaş, Haldun M.; Gotchev, A.Computation of the diffraction field from a given set of arbitrarily distributed data points in space is an important signal processing problem arising in digital holographic 3D displays. The field arising from such distributed data points has to be solved simultaneously by considering all mutual couplings to get correct results. In our approach, the discrete form of the plane wave decomposition is used to calculate the diffraction field. Two approaches, based on matrix inversion and on projections on to convex sets (POCS), are studied. Both approaches are able to obtain the desired field when the number of given data points is larger than the number of data points on a transverse cross-section of the space. The POCS-based algorithm outperforms the matrix-inversion-based algorithm when the number of known data points is large.Item Open Access Diffraction from a wavelet point of view(Optical Society of America, 1993-06-01) Onural, L.The system impulse response representing the Fresnel diffraction is shown to form a wavelet family of functions. The scale parameter of the wavelet family represents the depth (distance). This observation relates the diffraction-holography-related studies and the wavelet theory. The results may be used in various optical applications such as designing robust volume optical elements for optical signal processing and finding new formulations for optical inverse problems. The results also extend the wavelet concept to the nonbandpass family of functions with the implication of new applications in signal processing. The presented wavelet structure, for example, is a tool for space-depth analysis.Item Open Access Digital decoding of in-line holograms(SPIE, 1987) Onural, L.; Scott, P. D.Digitally sampled in-line holograms may be linearly filtered to reconstruct a representation of the original object distribution, thereby decoding the information contained in the hologram. The decoding process is performed by digital computation rather than optically. Substitution of digital for optical decoding has several advantages, including selective suppression of the twin-image artifact, elimination of the far-field requirement, and automation of the data reduction and analysis process. The proposed filter is a truncated series expansion of the inverse of that operator that maps object opacity function to hologram intensity. The first term of the expansion is shown to be equivalent to conventional (optical) reconstruction, with successive terms increasingly suppressing the twin image. The algorithm is computationally efficient, requiring only a single fast Fourier transform pair.Item Open Access Digital holographic three-dimensional video displays(IEEE, 2011-02-04) Onural, L.; Yaras, F.; Kang, H.Holography aims to record and regenerate volume filling light fields to reproduce ghost-like 3-D images that are optically indistinguishable from their physical 3-D originals. Digital holographic video displays are pixelated devices on which digital holograms can be written at video rates. Spatial light modulators (SLMs) are used for such purposes in practice; even though it is desirable to have SLMs that can modulate both the phase and amplitude of the incident light at each pixel, usually amplitude-only or phase-only SLMs are available. Many laboratories have reported working prototypes using different designs. Size and resolution of the SLMs are quite demanding for satisfactory 3-D reconstructions. Space–bandwidth product (SBP) seems like a good metric for quality analysis. Even though moderate SBP is satisfactory for a stationary observer with no lateral or rotational motion, the required SBP quickly increases when such motion is allowed. Multi-SLM designs, especially over curved surfaces, relieve high bandwidth requirements, and therefore, are strong candidates for futuristic holographic video displays. Holograms are quite robust to noise and quantization. It is demonstrated that either laser or light-emitting diode (LED) illumination is feasible. Current research momentum is increasing with many exciting and encouraging results.Item Open Access Estimation of depth fields suitable for video compression based on 3-D structure and motion of objects(Institute of Electrical and Electronics Engineers, 1998-06) Alatan, A. A.; Onural, L.Intensity prediction along motion trajectories removes temporal redundancy considerably in video compression algorithms. In three-dimensional (3-D) object-based video coding, both 3-D motion and depth values are required for temporal prediction. The required 3-D motion parameters for each object are found by the correspondence-based E-matrix method. The estimation of the correspondences - two-dimensional (2-D) motion field - between the frames and segmentation of the scene into objects are achieved simultaneously by minimizing a Gibbs energy. The depth field is estimated by jointly minimizing a defined distortion and bitrate criterion using the 3-D motion parameters. The resulting depth field is efficient in the rate-distortion sense. Bit-rate values corresponding to the lossless encoding of the resultant depth fields are obtained using predictive coding; prediction errors are encoded by a Lempel-Ziv algorithm. The results are satisfactory for real-life video scenes.Item Open Access Evaluation of the validity of the scalar approximation in optical wave propagation using a systems approach and an accurate digital electromagnetic model(Taylor and Francis Ltd., 2016) Kulce, O.; Onural, L.; Özaktaş, Haldun M.The cause and amount of error arising from the use of the scalar approximation in monochromatic optical wave propagation are discussed using a signals and systems formulation. Based on Gauss’s Law, the longitudinal component of an electric field is computed from the transverse components by passing the latter through a two input single output linear shift-invariant system. The system is analytically characterized both in the space and frequency domains. For propagating waves, the large response for the frequencies near the limiting wave number indicates the small angle requirement for the validity of the scalar approximation. Also, a discrete simulator is developed to compute the longitudinal component from the transverse components for monochromatic propagating electric fields. The simulator output helps to evaluate the validity of the scalar approximation when the system output cannot be analytically calculated. © 2016 Informa UK Limited, trading as Taylor & Francis Group.Item Open Access Exact analysis of the effects of sampling of the scalar diffraction field(Optical Society of America, 2007) Onural, L.If the sampled diffraction pattern due to a planar object is used to reconstruct the object pattern by backpropagation, the obtained pattern is no longer the same as the original. The effect of such sampling on the reconstruction is analyzed, The formulation uses the plane-wave expansion, and therefore the provided solution is exact for wave propagation in media where scalar wave propagation is valid. In contrast to the sampling effects under the Fresnel approximation, the exact solution indicates that there are no modulated replicas of the original object in the reconstructed pattern. Rather, the distortion is in the form of modulated, translated, and dispersed versions of the original.Item Open Access Exact diffraction calculation from fields specified over arbitrary curved surfaces(Elsevier, 2011-07-30) Esmer, G. B.; Onural, L.; Özaktaş, Haldun M.Calculation of the scalar diffraction field over the entire space from a given field over a surface is an important problem in computer generated holography. A straightforward approach to compute the diffraction field from field samples given on a surface is to superpose the emanated fields from each such sample. In this approach, possible mutual interactions between the fields at these samples are omitted and the calculated field may be significantly in error. In the proposed diffraction calculation algorithm, mutual interactions are taken into consideration, and thus the exact diffraction field can be calculated. The algorithm is based on posing the problem as the inverse of a problem whose formulation is straightforward. The problem is then solved by a signal decomposition approach. The computational cost of the proposed method is high, but it yields the exact scalar diffraction field over the entire space from the data on a surface.Item Open Access Exact solution for scalar diffraction between tilted and translated planes using impulse functions over a surface(Optical Society of America, 2011-02-04) Onural, L.The diffraction relation between a plane and another plane that is both tilted and translated with respect to the first one is revisited. The derivation of the result becomes easier when the impulse function over a surface is used as a tool. Such an approach converts the original 2D problem to an intermediate 3D problem and thus allows utilization of easy-to-interpret Fourier transform properties due to rotation and translation. An exact solution for the scalar monochromatic propagating waves case when the propagation direction is restricted to be in the forward direction is presented.
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