Selected Publications
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Yamaguchi, Wilburn , Z. Cao & E. Ofek Video-based modeling of dynamic hair Accepted to Pacific-Rim Symposium on Image & Video Technology 2009, Tokyo, Japan
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P. Mishra, E.
Ofek & G. Kimchi Validation of Vector Data using Oblique Images Accepted to ACM SIGGIS 2008, CA USA Oblique images are aerial photographs taken at oblique angles to the earth’s surface. Projections of vector and other geospatial data in these images depend on camera parameters, positions of the entities, surface terrain, and visibility. This paper presents a robust and scalable algorithm to detect inconsistencies in vector data using oblique images. The algorithm uses image descriptors to encode the local appearance of a geospatial entity in images. These image descriptors combine color, pixel-intensity gradients, texture, and steerable filter responses. A Support Vector Machine classifier is trained to detect image descriptors that are not consistent with underlying vector data, digital elevation maps, building models, and camera parameters. In this paper, we train the classifier on visible road segments and non-road data. Thereafter, the trained classifier detects inconsistencies in vectors, which include both occluded and misaligned road segments. The consistent road segments validate our vector, DEM, and 3-D model data for those areas while inconsistent segments point out errors. We further show that a search for descriptors that are consistent with visible road segments in the neighborhood of a misaligned road yields the desired road alignment that is consistent with pixels in the image. |
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J. Xiao, T. Fang.
P. Tan, Z. Peng, E. Ofek & L. Quan Image Based Facade Modeling Accepted to ACM SIGGRAPH Asia 2008, Singapure We propose in this paper a semi-automatic image-based approach that uses images captured along the streets, and relies on structure from motion to automatically recover the camera positions and point clouds as the initial stage for the modeling. We start a building facade as a flat rectangular plane or a developable surface, and the texture image of the flat facade is composited from the multiple visible images with handling of occluding objects. A facade is then decomposed and structured into a Directed Acyclic Graph of rectilinear elementary patches. The decomposition is carried out top-down by a recursive subdivision, and followed by a bottom-up merging with the detection of the architectural bilateral symmetry and repetitive patterns. Each subdivided patch of the flat facade is augmented with the depth that is optimized from the 3D points. Our system also allows the user to easily provide feedbacks in the 2D image space for the proposed decomposition and augmentation. Finally, our approach is demonstrated on a large number of facades from a variety of street-side images. |
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H. Wang,
H. Hoppe, Y. Wexler and E. Ofek
Factoring Repeated Content Within
and Among Images (11M)
ACM SIGGRAPH 2008, Los Angeles USA We reduce transmission bandwidth and memory
space for images by factoring their repeated content. A transform map and a
condensed epitome are created such that all image blocks can be reconstructed
from transformed epitome patches. The transforms may include affine deformation
and color scaling to account for perspective and tonal variations across the
image. The factored representation allows efficient random-access through a
simple indirection, and can therefore be used for real-time texture mapping
without expansion in memory. Our scheme is orthogonal to traditional image
compression, in the sense that the epitome is amenable to further compression
such as DXT. Moreover it allows a new mode of progressivity, whereby generic
features appear before unique detail. Factoring is also effective across a
collection of images, particularly in the context of image-based rendering.
Eliminating redundant content lets us include textures that are several times
as large in the same memory space. |
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B. Epshtein, E. Ofek, Y. Wexler and P. Zhang Hierarchical photo organization using geo-relevance ACM GIS 2007, Seattle WA, USA
We present a novel framework for organizing large collections of images in a hierarchical way, based on scene semantics. Rather than score images directly, we use them to score the scene in order to identify typical views and important locations which we term Geo-Relevance. This is done by relating each image with its viewing frustum which can be readily computed for huge collections of images nowadays. The frustum contains much more information than only camera position that has been used so far. For example, it distinguishes between a photo of the Eiffel Tower and a photo of a garbage bin taken from the exact same place. The proposed framework enables a summarized display of the information and facilitates efficient browsing.
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N.Li, N. Moraveji, H. Kimura and E. Ofek Improving the Experience of Controlling Avatars in Camera-Based Games Using Physical Input The 14th ACM International Conference on Multimedia, Santa Barbara, CA, USA 2006
This paper investigates two methods of improving the user experience of camera-based interaction. First, problems that arise when avatars are designed to mimic a user’s physical actions are presented. Second, a solution is proposed: adding a layer of separation between user and avatar while retaining intuitive user control. Two methods are proposed for this separation: spatially and temporally. Implementations of these methods are then presented in the context of a simple game and evaluate their effect on performance and satisfaction. Results of a human subject experiment are presented, showing that reducing the amount of user control can maintain, and even improve, user satisfaction if the design of such a reduction is appropriate. This is followed by a discussion of how the findings inform camera-based game design.
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H. Jiang, E. Ofek, N. Moraveji and S. Yuanchun Direct Pointer: Direct Manipulation for Large Display Interaction using Handheld Cameras SIG CHI 2006, Montreal, Canada
This paper describes the design and evaluation of a technique, Direct Pointer, that enables users to interact intuitively with large displays using cameras equipped on handheld devices, such as mobile phones and personal digital assistant (PDA). In contrast to many existing interaction methods that attempt to address the same problem, ours offers direct manipulation of the pointer position with continuous visual feedback. The primary advantage of this technique is that it only requires equipment that is readily available: an electronic display, a handheld digital camera, and a connection between the two. No special visual markers in the display content are needed, nor are fixed cameras pointing at the display. We evaluated the performance of Direct Pointer as an interaction product, showing that it performs as well as comparable techniques that require more sophisticated equipment.
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Y. Matsushita, E. Ofek, X. Tang and H. Shum Full Frame Video Stabilization with Motion Inpainting IEEE PAMI 2006
Video stabilization is an important video enhancement technology which aims at removing annoying shaky motion from videos. We propose a practical and robust approach of video stabilization that produces full-frame stabilized videos with good visual quality. While most previous methods end up with producing low resolution stabilized videos, our completion method can produce full-frame videos by naturally filling in missing image parts by locally aligning image data of neighboring frames. To achieve this, motion inpainting is proposed to enforce spatial and temporal consistency of the completion in both static and dynamic image areas. In addition, image quality in the stabilized video is enhanced with a new practical deblurring algorithm. Instead of estimating point spread functions, our method transfers and interpolates sharper image pixels of neighboring frames to increase the sharpness of the frame. The proposed video completion and deblurring methods enabled us to develop a complete video stabilizer which can naturally keep the original image quality in the stabilized videos. The effectiveness of our method is confirmed by extensive experiments over a wide variety of videos. |
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Y. Wei, E. Ofek, L. Quan and H. Shum Modeling Hair from Multi Views SIGGRAPH 2005, Los Angeles, CA. |
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Y. Matsushita, E. Ofek, X. Tang and H. Shum Video Completion with Motion Inpainting for Video Stabilization CVPR 2005, San Diego, CA.
Video stabilization is an important video enhancement technology which aims at removing annoying shaky motion from videos. We propose a practical and robust approach of video stabilization that produces full-frame stabilized videos with good visual quality. While most previous methods end up with producing low resolution stabilized videos, our completion method can produce full-frame videos by naturally filling in missing image parts by locally aligning image data of neighboring frames. To achieve this, motion inpainting is proposed to enforce spatial and temporal consistency of the completion in both static and dynamic image areas. In addition, image quality in the stabilized video is enhanced with a new practical deblurring algorithm. Instead of estimating point spread functions, our method transfers and interpolates sharper image pixels of neighboring frames to increase the sharpness of the frame. The proposed video completion and deblurring methods enabled us to develop a complete video stabilizer which can naturally keep the original image quality in the stabilized videos. The effectiveness of our method is confirmed by extensive experiments over a wide variety of videos. |
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B. Chen, E. Ofek, H. Shum and M. Levoy Interactive Deformation of Light Fields SIGGRAPH I3D 2005, Washington D.C. |
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X. Cao, E. Ofek, and D. Vronay Evaluation of Alterantive Presentation Control Techniques. (PDF, 420K) SIG CHI 2005, Protland, OR.
This paper describes the design and evaluation of a technique, Direct Pointer, that enables users to interact intuitively with large displays using cameras equipped on handheld devices, such as mobile phones and personal digital assistant (PDA). In contrast to many existing interaction methods that attempt to address the same problem, ours offers direct manipulation of the pointer position with continuous visual feedback. The primary advantage of this technique is that it only requires equipments that are readily available: a large electronic display, a handheld camera, and a connection between the two. No special visual markers in the display content are needed, nor are fixed cameras pointing at the display. We evaluated the performance of Direct Pointer as an interaction product, showing that it performs as well as comparable techniques that require more sophisticated equipment. |
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R. Gvili, A. Kaplan, E. Ofek, G. Yahav Stereoscopic Displays and Applications: The Engineering Reality of Virtual Reality 2003 (Proceedings of SPIE/IS&T Volume 5006), San Jose, CA. |
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A. Redert, M. Op de Beeck, C. Fehn, W. IJsselsteijn, M. Pollefeys, L. J. Van Gool, E. Ofek, I. Sexton and P. Surman ATTEST: Advanced Three-dimensional Television System Technologies. 3DPVT 2002, Padova, Italy. |
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E. Ofek and A. Rappoport Interactive reflections on curved objects ACM SIGGRAPH 1998 Global view-dependent illumination phenomena,
in particular reflections, |
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E. Ofek, E. Shilat, A. Rappoport, and M. Werman.Multi-resolution Textures from Image Sequences (PDF, 515K)IEEE Computer Graphics and Applications 1997 |
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