Browsing by Author "Onural, Levent"
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Item Open Access Analysis of the complex light field generated by a deflectable mirror array device(SPIE, 2006) Ulusoy, Erdem; Onural, Levent; Özaktaş, Haldun M.An exact analysis of the scalar coherent monochromatic light field produced by a deflectable mirror array device is presented. The three-dimensional light field is related to the tilt angles of the mirrors. The first Rayleigh-Sommerfeld diffraction formula is used to model the diffraction. The analysis is carried out based on the assumption that the mirrors can be tilted with continuously varying angles, so the field produced by a finite (discrete) set of possible tilt angles is included as a special case.Item Open Access Analysis of the longitudinal component of the electric field generated by flat and pixelated liquid crystal displays(IEEE, 2016-07) Külçe, Onur; Onural, LeventThe longitudinal, z, component of the electric field is investigated for the pixelated and flat liquid crystal displays (LCDs) for monochromatic case. The pixelation process is assumed to occur in free space. The z component is computed in the Fourier domain by using Gauss's Law from the x and y components of the output electric field. The effect of the display parameters are discussed for a y polarized display in a phase only operation. It is found that, in the low frequency regions, the size of the region of the large magnitudes becomes smaller as the width of the active region increases. Moreover, the validity of the scalar theory for a single pixel is evaluated for varying pixel sizes. It is shown that, when the ratio of the width of the active region to wavelength is between 1.5 and 5, the error decays with oscillations between 43% and 5%. When that ratio is larger than 15, the error does not exceed 3%. © 2016 IEEE.Item Open Access An automated system for design-rule-based visual inspection of printed circuit boards(IEEE, 1991) Oğuz, Seyfullah Halit; Onural, LeventThe design and the implementation of an automated, design-rule-based, visual printed circuit board (PCB) inspection system are presented. The system employs mathematical-morphology-based image processing algorithms. This system detects PCB defects related to the conducting structures on PCBs by checking a set of geometric design rules. For this purpose, an image segmentation algorithm and a defect detection algorithm are designed. The defect detection algorithm is capable of verifying the minimum conductor spacing, minimum conductor trace width, and the minimum land width requirements on digital binary PCB images. Also, an existing defect detection algorithm is modified for its implementation in the system.Item Open Access Baǧlanırlıkla yönlendirilmiş uyarlamalı dalgacık dönüşümü ile üç boyutlu model sıkıştırılması(IEEE, 2007-06) Köse, Kıvanç; Çetin, A. Enis; Güdükbay, Uğur; Onural, LeventDikdörtgensel olmayan dalgacık dönüşümüne dayalı çok çözünürlüklü üç boyutlu model sıkıştırılması için iki yöntem önerilmektedir. Bunlar Sıradüzensel Ağaç Yapılarının Kümelere Bölütlenmesi (Set Partitioning In Hierarchical Trees - SPIHT) ve JPEG2000 tekniklerine dayanmaktadır. Üç boyutlu modeller düzenli ızgara yapılar üzerinde tanımlı iki boyutlu imgelere dönüştürülmekte, ve bu gösterim bağlanırlıkla yönlendirilmiş uyarlamalı dalgacık dönüşümünden geçirilerek ortaya çıkan dalgacık kümesi verisi SPITH veya JPEG2000 yöntemlerinden biri uygulanarak bit dizgisine dönüştürülmektedir. SPIHT ile elde edilen bit dizgisinin değişik uzunluklardaki bölümlerinden modelin değişik çözünürlüklerde geri çatmak mümkün olduğundan önerilen bu yöntem modellerin aşamalı gösterimine olanak sağlamaktadır. Dalgacık dönüşümü verilerinin SPIHT ile kodlanmasıyla elde edilen sonuç JPEG2000 ve MPEG-3DGC ile yapılan kodlamanın sonucundan daha başarılı olmuştur. Two compression frameworks that are based on a Set Partitioning In Hierarchical Trees (SPIHT) and JPEG2000 methods are proposed. The 3D mesh is first transformed to 2D images on a regular grid structure. Then, this image-like representation is wavelet transformed employing an adaptive predictor that takes advantage of the connectivity information of mesh vertices. Then SPIHT or JPEG2000 is applied on the wavelet domain data. The SPIHT based method is progressive because the resolution of the reconstructed mesh can be changed by varying the length of the one-dimensional data stream created by SPIHT algorithm. The results of the SPIHT based algorith is observed to be superior to JPEG200 based mesh coder and MPEG-3DGC in rate-distortion.Item Open Access Bessel functions-based reconstruction of non-uniformly sampled diffraction fields(IEEE, 2007) Uzunov, V.; Esmer, G. Bora; Gotchev, A.; Onural, Levent; Özaktaş, Haldun M.A discrete computational model for the diffraction process is essential in forward problems related to holographic TV. The model must be as general as possible, since the shape of the displayed objects does not bear any restrictions. We derive a discrete diffraction model which suits the problem of reconstruction of diffraction fields from a set of non-uniformly distributed samples. The only restriction of the model is the wave nature of the field. The derivation takes advantage of changing the spatial and frequency coordinates to polar form and ends up with a model stated in terms of Bessel functions. The model proves to be a separable orthogonal basis. It shows rapid convergence when evaluated in the framework of the non-uniform sampling problem.Item Open Access Capture, processing, and display of real-world 3D objects using digital holography(IEEE, 2010) Naughton, T.J.; Falldorf, C.; Onural, Levent; Ferraro P.; Depeursinge, C.; Krueger, S.; Emery, Y.; Hennelly, B.M.; Kujawifiska, M."Digital holography for 3D and 4D real-world objects' capture, processing, and display" (acronym "Real 3D") is a research project funded under the Information and Communication Technologies theme of the European Commission's Seventh Framework Programme, and brings together nine participants from academia and industry (see www.digitalholography.eu).This three-year project marks the beginning a long-term effort to facilitate the entry of a new technology (digital holography) into the three-dimensional capture and display markets. Its progress at the end of year 2 is summarised. © 2010 IEEE.Item Open Access Circularly configured multi-SLM holographic display system(IEEE, 2011) Yaraş, Fahri; Kang, Hoonjong; Onural, LeventThe designed circular holographic display system produces ghost-like 3D optical reconstructions of a computer generated 3D model. System uses six phase-only reflective-type spatial light modulators (SLMs) that are configured circularly. Alignment of the SLMs are successful and gap problem is solved by using half-mirrors. The total number of pixels of the resultant display is 11520 1080. Reconstructions show that increase in the viewing angle is significant compared to the single SLM case. With the help of the proposed system, observer can see the reconstructions binocularly. As a result, comfortable 3D perception is achieved. In order to avoid eye-hazard, LED illumination is also used as an alternative light source. Experimental results are satisfactory. Proposed system can be used as a holographic display system.Item Open Access Color holographic reconstruction using multiple SLMs and LED illumination(SPIE, 2009-01) Yaraş, Fahri; Onural, LeventA color holographic reconstruction technique by using three light emitting diodes (LEDs) is described. Reflective type phase-only spatial light modulators (SLMs) are used since they are suitable for in-line phase holograms. Gerchberg-Saxton iterative algorithm is used for computing phase holograms. Three phase holograms are calculated separately for red, green and blue colors, for a color reconstruction, and separately loaded to corresponding SLMs. Three LEDs are used for illuminating those phase holograms and reconstructions are combined and captured. Experimental results are satisfactory. © 2009 SPIE-IS&T.Item Open Access Computation of holographic patterns between tilted planes(SPIE - International Society for Optical Engineering, 2006-05) Esmer, Gökhan Bora; Onural, LeventComputation of the diffraction pattern that gives the desired reconstruction of an object upon proper illumination is an important process in computer generated holography. A fast computational method, based on the plane wave decomposition of 3D field in free-space, is presented to find the desired diffraction pattern. The computational burden includes two FFT algorithms in addition to a shuffling of the frequency components that needs an interpolation in the frequency domain. The algorithm is based on the exact diffraction formulation; there is no need for Fresnel or Fraunhofer approximations. The developed model is utilized to calculate the scalar optical diffraction between tilted planes for monochromatic light. The performance of the presented algorithm is satisfactory for tilt angles up to 60°.Item Open Access Connectivity-guided adaptive lifting transform for image like compression of meshes(IEEE, 2007-05) Köse, Kıvanç; Çetin, A. Enis; Güdükbay, Uğur; Onural, LeventWe propose a new connectivity-guided adaptive wavelet transform based mesh compression framework. The 3D mesh is first transformed to 2D images on a regular grid structure by performing orthogonal projections onto the image plane. Then, this image-like representation is wavelet transformed using a lifting structure employing an adaptive predictor that takes advantage of the connectivity information of mesh vertices. Then the wavelet domain data is encoded using "Set Partitioning In Hierarchical Trees" (SPIHT) method or JPEG2000. The SPIHT approach is progressive because the resolution of the reconstructed mesh can be changed by varying the length of the 1D data stream created by the algorithm. In JPEG2000 based approach, quantization of the coefficients determines the quality of the reconstruction. The results of the SPIHT based algorithm is observed to be superior to JPEG200 based mesh coder and MPEG-3DGC in rate-distortion.Item Open Access Current research activities on holographic video displays(SPIE, 2010) Onural, Levent; Yaraş, Fahri; Kang, Hoonjong"True 3D" display technologies target replication of physical volume light distributions. Holography is a promising true 3D technique. Widespread utilization of holographic 3D video displays is hindered by current technological limits; research activities are targeted to overcome such difficulties. Rising interest in 3D video in general, and current developments in holographic 3D video and underlying technologies increase the momentum of research activities in this field. Prototypes and recent satisfactory laboratory results indicate that holographic displays are strong candidates for future 3D displays.Item Open Access Design and implementation of a DMD based volumetric 3D display(IEEE, 2008-05) Yücesoy, Veysel; Tunaoǧlu, Doruk; Kovachev, Metodi; Ilieva, Rossitza; Onural, LeventA real image swept-volume volumetric display is developed. A piston type moving screen is used to obtain the desired volume. A commercially available DMD device is used to project 2D slices of a 3D frame. There is a varying magnification effect during the projection because of the optical design of the system; raw 3D video frames are processed by a software to generate the appropriate 2D slices by also correcting the magnification. Synchronization between the hardware and the software is achieved via a microcontroller. The overall system is capable of printing 12 3D frames per second where a 3D frame consists of 90 2D slices with a resolution varying from 512x512 to 450x450 (approx. 20M voxels per one 3D frame). Although some flickering effect is observed due to rather low 3D frame rate, results are visually satisfactory. ©2008 IEEE.Item Open Access Design and implementation of a general purpose VLSI median filter unit and its applications(IEEE, 1989) Karaman, Mustafa; Onural, Levent; Atalar, AbdullahA VLSI median filter unit has been designed and implemented in 3-μ m M2 CMOS, using full-custom VLSI design techniques. The unit consists of two single-chip median filters, one extensible and one real-time. The chips are bit-level pipelined systolic structures based on odd/even transposition sorting. The extensible chip is designed for applications requiring variable window sizes and variable word-lengths, whereas the other one is for real-time applications. Various median filtering techniques are easily realized by using the designed chips together with reasonable external hardware.Item Open Access Design of a 360-degree holographic 3D video display using commonly available display panels and a paraboloid mirror(SPIE, 2017) Onural, LeventEven barely acceptable quality holographic 3D video displays require hundreds of mega pixels with a pixel size in the order of a fraction of a micrometer, when conventional flat panel SLM arrangement is used. Smaller pixel sizes are essential to get larger diffraction angles. Common flat display panels, however, have pixel sizes in the order of tens of micrometers, and this results in diffraction angles in the order of one degree. Here in this design, an array of commonly available (similar to high-end mobile phone display panels) flat display panels, is used. Each flat panel, as an element of the array, directs its outgoing low-diffraction angle light beam to corresponding small portion of a large size paraboloid mirror; the mirror then reflects the slowly-expanding, information carrying beam to direct it at a certain exit angle; this beam constitutes a portion of the final real ghost-like 3D holographic image. The collection of those components from all such flat display panels cover the entire 360-degrees and thus constitute the final real 3D table-top holographic display with a 360-degrees viewing angle. The size of the resultant display is smaller compared to the physical size of the paraboloid mirror, or the overall size of the display panel array; however, an acceptable size table top display can be easily constructed for living-room viewing. A matching camera can also be designed by reversing the optical paths and by replacing the flat display panels by flat wavefront capture devices.Item Open Access Diffraction and holography from a signal processing perspective(SPIE, 2006) Onural, Levent; Özaktaş, Haldun M.The fact that plane waves are solutions of the Helmholtz equation in free space allows us to write the exact solution to the diffraction problem as a superposition of plane waves. The solution of other related problems can also be expressed in similar forms. These forms are very well suited for directly importing various signal processing tools to diffraction related problems. Another signal processing-diffraction link is the application of novel sampling theorems and procedures in signal processing to diffraction for the purpose of more convenient and efficient discrete representation and the use of associated computational algorithms. Another noteworthy link between optics and signal processing is the fractional Fourier transform. Revisiting diffraction from a modern signal processing perspectiv is likely to yield both interesting viewpoints and improved techniques.Item Open Access Effect of sample locations on computation of the exact scalar diffraction field (in English)(IEEE, 2012) Esmer, G. B.; Özaktaş, Haldun M.; Onural, LeventComputer generated holography is one of common methods to obtain three-dimensional visualization. It can be explained by behavior of propagating waves and interference. To calculate the scalar diffraction pattern on a hologram, there are myriad of algorithms in the literature. Some of them employ several approximations, so the calculated fields may not be the exact scalar diffraction field. However, there are algorithms to compute the exact scalar diffraction field with some limitations on the distribution of the given samples over the space. These algorithms are based on "field model" approach. The performance of an algorithm, based on field model, is investigated according to the distribution of given samples over the space. From the simulations, it was observed that the cumulative information provided by the given samples has to be enough to solve the inverse scalar diffraction field. The cumulative information can be increased by having more samples, but there are some scenarios that differential information obtained from the given samples can be infinitesimal, thus the exact diffraction field may not be computed. © 2012 IEEE.Item Open Access Feature issue of digital holography and 3D imaging (DH) introduction(Optical Society of America (OSA), 2014-07) Hayasaki, Y.; Zhou, C.; Popescu, G.; Onural, LeventThe OSA Topical Meeting "Digital Holography and 3D Imaging (DH)," was held in Seattle, Washington, July 13-17, 2014. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. This year Optics Express (OE) and AO jointly decided to have one such feature issue in each journal. The DH meeting will continue in the future, as expected, and the next meeting is scheduled to be held on 24-28 May 2015, in Shanghai Institute of Optics and Fine Mechanics, Shanghai, China. © 2014 Optical Society of AmericaItem Open Access Filtering in fractional Fourier domains and their relation to chirp transforms(IEEE, 1994-04) Özaktaş, Haldun M.; Barshan, Billur; Onural, Levent; Mendlovic, D.Fractional Fourier transforms, which are related to chirp and wavelet transforms, lead to the notion of fractional Fourier domains. The concept of filtering of signals in fractional domains is developed, revealing that under certain conditions one can improve upon 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 A general purpose VLSI median filter and its applications for image processing(IEEE, 1989) Karaman, Mustafa; Onural, Levent; Atalar, AbdullahA general-purpose median filter configuration consisting of two single-chip median filters is proposed. One of the chips is designed for applications requiring variable word-length and variable window size, whereas the other is for real-time applications. The architectures of the chips are based on odd/even transposition sorting. The chips are implemented in 3-μm M2CMOS using full-custom VLSI design techniques. The chips together with a reasonable external hardware can be used for the realizations of many median filtering techniques. The VLSI design procedure of the chips and their applications to different median filtering techniques for image processing are presented.Item Open Access Generation of a polarized optical field from a given scalar field for wide-viewing-angle holographic displays(Elsevier, 2020-08-20) Kulce, O.; Onural, LeventAlthough the scalar wave theory does not fully describe the nature of the light, which is a vector wave field, it is common to characterize the optical field propagated from an object as a scalar wave in 3DTV research. A given scalar wave field is usually directly mapped to the transverse field components of a simply polarized optical field during the generation of the optical field by a holographic 3D display; this procedure gives accurate results in terms of the optical intensity if the field is paraxial. However, due to the nonnegligibly large longitudinal component of the vector field, this method fails in wide-angle fields. In order to generate a polarized optical field which has the same resultant effect as prescribed by a wide-angle scalar field, we extend this simple polarization approach to tilted and rotated planes. That is, we first put a constraint on the generated vector wave field such that each plane wave component has a simple polarization relation at its locally transverse plane. Then, we map the complex plane wave amplitudes of a given scalar field to the plane wave amplitudes of locally transverse field components of the polarization-constrained optical field. As a consequence of the developed mapping, for an observer which is located at a tilted and rotated plane and captures a locally paraxial segment of the incoming wave field, the intended scalar intensity results can also be obtained in wide-viewing-angle 3D holographic displays. The developed model is valid if the chosen local coordinate frames of the locally transverse planes of the propagating plane waves vary slowly as the propagation direction changes. For a 3DTV setup where the display is located at a z-plane and the observers are located away from the z-axis, an analytical representation for appropriate coordinate frames is developed. For the same setup, computer simulation results showed that the excessive amplification of the longitudinal component due to the conventional mapping does not arise in the proposed method and the desired scalar results are observed. Moreover, since the determined polarization state is preserved at each tilted and rotated plane, the new model can also be used in an optical setup where the polarization information is important. As a result, the proposed mapping enables the scalar wave theory to be used in wide-viewing angle holographic display applications under the given constraints.