Browsing by Subject "Computer Graphics"

Now showing 1 - 12 of 12

Open Access
Automatic determination of navigable areas, pedestrian detection, and augmentation of virtual agents in real crowd videos
(2018-12) Doğan, Yalım
Crowd simulations imitate the behavior of crowds and individual agents in the crowd with personality and appearance, which determines the overall model of a multi-agent system. In such studies, the models are often compared with real-life scenarios for assessment. Yet apart from side-by-side comparison and trajectory analysis, there are no practical, out-of-the-box tools to test how a given arbitrary model simulate the scenario that takes place in the real world. We propose a framework for augmenting virtual agents in real-life crowd videos. The framework locates the navigable areas on the ground plane using the automaticallyextracted detection data of the pedestrians in the crowd video. Then it places the three-dimensional (3D) models of real pedestrians in the 3D model of the scene. An interactive user interface is provided for users to add and control virtual agents, which are simulated together with detected real pedestrians using collision avoidance algorithms.
Open Access
Content-based retrieval of historical Ottoman documents stored as textual images
(IEEE, 2004) Şaykol, E.; Sinop, A. K.; Güdükbay, Uğur; Ulusoy, Özgür; Çetin, A. Enis
There is an accelerating demand to access the visual content of documents stored in historical and cultural archives. Availability of electronic imaging tools and effective image processing techniques makes it feasible to process the multimedia data in large databases. In this paper, a framework for content-based retrieval of historical documents in the Ottoman Empire archives is presented. The documents are stored as textual images, which are compressed by constructing a library of symbols occurring in a document, and the symbols in the original image are then replaced with pointers into the codebook to obtain a compressed representation of the image. The features in wavelet and spatial domain based on angular and distance span of shapes are used to extract the symbols. In order to make content-based retrieval in historical archives, a query is specified as a rectangular region in an input image and the same symbol-extraction process is applied to the query region. The queries are processed on the codebook of documents and the query images are identified in the resulting documents using the pointers in textual images. The querying process does not require decompression of images. The new content-based retrieval framework is also applicable to many other document archives using different scripts.
Open Access
Creating a presentation format of interactive media for innovative products
(1994) Sinman, Aslı
In this work, an interactive presentation format to give information about an innovative product is developed. Innovation process is also discussed for communication of users and designers. Accessing the original needs of potential users by making them active participants through this interactive presentation is considered. Target audience for the innovative product is defined with analysing them in terms of education, culture, social status, and age. Besides the presentation format, the visual style is designed which should be consistent and visible. Construction of graphics, text and animation elements of the presentation on a two dimensional computer graphics interface and attractive graphic format for receiving participation of the users are studied as well. Newton, a palm sized electronic notebook from Apple is selected as the irmovative product, to be analysed with the defined presentation format. Within the scope of a graphic designer or/and stack designer, a detailed story board of the whole presentation is developed.
Open Access
Direct volume rendering of unstructured grids
(Pergamon Press, 2003) Berk, Hakan; Aykanat, Cevdet; Güdükbay, Uğur
This paper investigates three categories of algorithms for direct volume rendering of unstructured grids, which are image-space, object-space, and hybrid methods. We propose three new algorithms. Cell Projection algorithm, which falls into object-space category, is capable of rendering non-convex meshes through a simple yet efficient sorting schema that exploits both image and object space coherencies. Existing hybrid methods use object-then-image traversal order that enforces the processing of each cell. Thus, these algorithms perform redundant operations and do not support early ray termination. We propose a hybrid method, called Span-Buffer Ray Casting (SBRC), that can support early ray termination discarding redundant operations by employing image-then-object traversal order. Another hybrid method, called Koyamada-SBRC (K-SBRC), is proposed with the motivation of refining image-space and hybrid methods to extract the best features of them. This method is developed by blending SBRC approach with Koyamada's algorithm, which is an efficient image-space algorithm. All proposed algorithms are capable of handling acyclic non-convex meshes and generating images of acceptable quality. SBRC and K-SBRC algorithms have the additional capabilities of rendering cyclic meshes and supporting early ray termination. The proposed algorithms and Koyamada's algorithm are implemented and experimented in a common framework for analyzing their relative performance. © 2003 Elsevier Science Ltd. All rights reserved.
Open Access
Graph visualization toolkits
(IEEE, 2002) Dogrusoz, U.; Feng, Q.; Madden, B.; Doorley, M.; Frick, A.
The Graph Layout Toolkit and Graph Editor Toolkit, which provide a framework for graph visualization useful in a broad array of application areas are introduced. As such, an architectural overview of these tools is presented and discusses the challenges encountered during implementation and integration of theory and research results into such tools. In particular, the automatic graph layout and labeling algorithms and complexity management techniques are discussed. In addition, some examples of applications using these tools are presented.
Open Access
Hair motion simulation
(Springer, 2004) Sahillioğlu, Y.; Özgüç, B.
Hair motion simulation in computer graphics has been an attraction for many researchers. The application we have developed has been inspired by the related previous work as well as our own efforts in finding useful algorithms to handle this problem. The work we present uses a set of representations, including hair strands, clusters and strips, that are derived from the same underlying base skeleton, where this skeleton is animated by physical, i.e. spring, forces. © Springer-Verlag 2004.
Open Access
A parallel progressive radiosity algorithm based on patch data circulation
(Pergamon Press, 1996) Aykanat, Cevdet; Çapin, T. K.; Özgüç, B.
Abstract - Current research on radiosity has concentrated on increasing the accuracy and the speed of the solution. Although algorithmic and meshing techniques decrease the execution time, still excessive computational power is required for complex scenes. Hence, parallelism can be exploited for speeding up the method further. This paper aims at providing a thorough examination of parallelism in the basic progressive refinement radiosity, and investigates its parallelization on distributed-memory parallel architectures. A synchronous scheme, based on static task assignment, is proposed to achieve better coherence for shooting patch selections. An efficient global circulation scheme is proposed for the parallel light distribution computations, which reduces the total volume of concurrent communication by an asymptotical factor. The proposed parallel algorithm is implemented on an Intel's iPSC/2 hypercube multicomputer. Load balance qualities of the proposed static assignment schemes are evaluated experimentally. The effect of coherence in the parallel light distribution computations on the shooting patch selection sequence is also investigated. Theoretical and experimental evaluation is also presented to verify that the proposed parallelization scheme yields equally good performance on multicomputers implementing the simplest (e.g. ring) as well as the richest (e.g. hypercube) interconnection topologies. This paper also proposes and presents a parallel load re-balancing scheme which enhances our basic parallel radiosity algorithm to be usable in the parallelization of radiosity methods adopting adaptive subdivision and meshing techniques. Copyright © 1996 Elsevier Science Ltd.
Open Access
Right-triangular subdivision for texture mapping ray-traced objects
(Springer, 1998) Akdemir, U.; Özgüç, B.; Güdükbay, Uğur; Selçuk, A.
The introduction of global illumination and texture mapping enabled the generation of high-quality, realistic looking images of computer graphics models. We describe a fast and efficient 2D texture mapping algorithm that uses triangle-to-triangle mapping, taking advantage of mapping an arbitrary triangle to a right triangle. This requires fewer floating point operations for finding the 2D texture coordinates and little preprocessing and storage. Texture mapping is combined with ray tracing for better visual effects. A filtering technique alternative to area sampling is developed to avoid aliasing artifacts. This technique uses linear eye rays, and only one eye ray per pixel is fired. A uniform supersampling filtering technique eliminates aliasing artifacts at the object edges.
Open Access
A spring force formulation for elastically deformable models
(Pergamon Press, 1997) Güdükbay, Uğur; Özgüç, B.; Tokad, Y.
Continuous deformable models are generally represented using a grid of control points. The elastic properties are then modeled using the interactions between these points. The formulations based on elasticity theory express these interactions using stiffness matrices. These matrices store the elastic properties of the models and they should be evolved in time according to changing elastic properties of the models. However, forming the stiffness matrices at any step of an animation is very difficult and sometimes the differential equations that should be solved to produce animation become ill-conditioned. Instead of modeling the elasticities using stiffness matrices, the interactions between model points could be expressed in terms of external spring forces. In this paper, a spring force formulation for animating elastically deformable models is presented. In this formulation, elastic properties of the materials are represented as external spring forces as opposed to forming complicated stiffness matrices. © 1997 Elsevier Science Ltd.
Open Access
Stereoscopic view-dependent visualization of terrain height fields
(IEEE, 2002) Güdükbay, Uğur; Yilmaz, T.
Visualization of large geometric environments has always been an important problem of computer graphics. In this paper, we present a framework for the stereoscopic view-dependent visualization of large scale terrain models. We use a quadtree based multiresolution representation for the terrain data. This structure is queried to obtain the view-dependent approximations of the terrain model at different levels of detail. In order not to lose depth information, which is crucial for the stereoscopic visualization, we make use of a different simplification criterion, namely, distance-based angular error threshold. We also present an algorithm for the construction of stereo pairs in order to speed up the view-dependent stereoscopic visualization. The approach we use is the simultaneous generation of the triangles for two stereo images using a single draw-list so that the view frustum culling and vertex activation is done only once for each frame. The cracking problem is solved using the dependency information stored for each vertex. We eliminate the popping artifacts that can occur while switching between different resolutions of the data using morphing. We implemented the proposed algorithms on personal computers and graphics workstations. Performance experiments show that the second eye image can be produced approximately 45 percent faster than drawing the two images separately and a smooth stereoscopic visualization can be achieved at interactive frame rates using continuous multiresolution representation of height fields.
Open Access
A text, image, and graphics editor
(1991) Coşar, A.; Özgüç, B.
[No abstract available]
Open Access
Visual attention models and applications to 3D computer graphics
(2012) Bülbül, Muhammed Abdullah
3D computer graphics, with the increasing technological and computational opportunities, have advanced to very high levels that it is possible to generate very realistic computer-generated scenes in real-time for games and other interactive environments. However, we cannot claim that computer graphics research has reached to its limits. Rendering photo-realistic scenes still cannot be achieved in real-time; and improving visual quality and decreasing computational costs are still research areas of great interest. Recent e orts in computer graphics have been directed towards exploiting principles of human visual perception to increase visual quality of rendering. This is natural since in computer graphics, the main source of evaluation is the judgment of people, which is based on their perception. In this thesis, our aim is to extend the use of perceptual principles in computer graphics. Our contribution is two-fold: First, we present several models to determine the visually important, salient, regions in a 3D scene. Secondly, we contribute to use of de nition of saliency metrics in computer graphics. Human visual attention is composed of two components, the rst component is the stimuli-oriented, bottom-up, visual attention; and the second component is task-oriented, top-down visual attention. The main di erence between these components is the role of the user. In the top-down component, viewer's intention and task a ect perception of the visual scene as opposed to the bottom-up component. We mostly investigate the bottom-up component where saliency resides. We de ne saliency computation metrics for two types of graphical contents. Our rst metric is applicable to 3D mesh models that are possibly animating, and it extracts saliency values for each vertex of the mesh models. The second metric we propose is applicable to animating objects and nds visually important objects due to their motion behaviours. In a third model, we present how to adapt the second metric for the animated 3D meshes. Along with the metrics of saliency, we also present possible application areas and a perceptual method to accelerate stereoscopic rendering, which is based on binocular vision principles and makes use of saliency information in a stereoscopic rendering scene. Each of the proposed models are evaluated with formal experiments. The proposed saliency metrics are evaluated via eye-tracker based experiments and the computationally salient regions are found to attract more attention in practice too. For the stereoscopic optimization part, we have performed a detailed experiment and veri ed our model of optimization. In conclusion, this thesis extends the use of human visual system principles in 3D computer graphics, especially in terms of saliency.