Publications
Home Short CV Publications Projects Misc Gallery

Z. Karni, L. Shapira, "Visualization and exploration for recommender systems in enterprise organization", SPIE Electonic Imaging, 2013.

Recommender systems seek to predict the interest a user would find in an item, person or social element they had not yet considered, based upon the properties of the item, the user's past experience and similar users. However, recommended items are often presented to the user with no context and no ability to influence the results. We present a novel visualization technique for recommender systems in which, a user can see the items recommended for him, and understand why they were recommended. Focusing on a user, we render a planar visualization listing a set of recommended items. The items are organized such that similar items reside nearby on the screen, centered around real-time generated categories. We use a combination of iconography, text and tag clouds, with maximal use of screen real estate, and keep items from overlapping to produce our results. We apply our visualization to expert relevance maps in the enterprise and a book recommendation system for consumers. The latter is based on Shelfari, a social network for reading and books.

Z. Karni, M. Fischer, A. Cardozo, G.E. de Paula, D. Shaked, R. Grohs, "Seamless Publication Using 3D Proofing", The 28th International Conference on Digital Printing Technologies, 2012.

The main motivation of this work is to expose professional level commercial print services to broad non-professional markets. In spite of increasing simplicity in content creation due to advances in authoring tools, publishing is still complex and reserved for professionals. To that end, there is high potential value in eliminating or reducing the barriers for non-experts to submit jobs for commercial printing, and in seamlessly connecting new non-professional content sources to the commercial printing environments. Our solution simplifies and automates the submission process by providing a workflow to replace the complex interaction between print buyers and commercial print experts. A key enabler for this workflow is an interactive and intuitive interface, which provides a soft proof of the finished product by a high-fidelity 2.5D/3D interactive model that captures the geometry and dynamic layout of the print product.

Z. Karni, A. Gaash, "SmartFit: automatic photo fitting for variable data printing", SPIE Electonic Imaging, 2012.

We present an algorithm for smart image fitting: changing the size of an image so that it may fit "naturally" within a given frame. As the frame's dimensions will generally differ from that of the image, the algorithm preserves important details in their original aspect ratio, while less important details undergo more substantial deformations. This problem is useful for many commercial print applications. One example is the HP SmartStream Designer, which is a tool to create variable and personalized content documents.

H. Nachlieli, Z. Karni, S. Raz, "Perception Guided Automatic Press Diagnosis", The 27th International Conference on Digital Printing Technologies, 2011.

We present an expert system for identifying print artifacts. The system balances between subjective sensitivities of print quality with an evaluation of the objective machine state. For example, fine bands may appear due to the mis-calibration of one machine component, while low contrast stains may exist on the same printing due to the state of another component. Different markets have different needs and hence may have different sensitivities to the same two artifacts. To achieve this balance, we combine an interactive expert system with an automatic analysis of dedicated print jobs. The expert system guides the user in classifying the print artifact according to his subjective sensitivities. Utilizing an inline-scanner enables automatic procedures for the detection of artifacts caused by an objective machine state. Benefits of the system include better control of print quality and better use of consumables.

D. Freedman, R. Chen, Z. Karni, C. Gotsman, L. Liu, "Content-Aware Image Resizing by Quadratic Programming", The 3rd Workshop on Non-Rigid Shape Analysis and Deformation Image Alighment, NORDIA, 2010.

We present a new method for content-aware image resizing based on a framework of global optimization. We show that the basic resizing problem can be formulated as a convex quadratic program. Furthermore, we demonstrate how the basic framework may be extended to prevent foldovers of the underlying mesh; encourage the magnification of salient regions; and preserve straight line structures. We show results demonstrating the effectiveness of the proposed method by comparing with four leading competitor methods.

Z. Karni, D. Freedman, D. Shaked, "Fast Inverse Halftoning", The 31st International Congress on Imaging Science, ICIS, 2010.

Printers use halftoning to render printed pages. This process is useful for many printing technologies which are binary in nature, as it allows the printer to deposit the ink as series of dots of constant darkness. Indeed, many of printing pipelines are based on this 1-bit framework; this unfortunately raises a critical problem when image processing operations that require the original 8-bit image must be performed. In this situation, what is required is the reconstruction of the 8-bit image from its halftoned version, a process referred to as "inverse halftoning". In this paper, we present a technique for fast inverse halftoning which given a dithered image together with the dithering mask that created it, approximates the original 8-bit image. The technique is elegant, and allows for generalizations to other inverse problems in which the exact details of the forward process are known. The algorithm is light computationally, and has been tested in practice. Results are shown, demonstrating the algorithm’s promise.

Z. Karni, D. Freedman, C. Gotsman, "Energy-Based Image Deformation", Eurographics Symposium on Geometry Processing, SGP, 2009.

We present a general approach to shape deformation based on energy minimization, and applications of this approach to the problems of image resizing and 2D shape deformation. Our deformation energy generalizes that found in the prior art, while still admitting an efficient algorithm for its optimization. The key advantage of our energy function is the flexibility with which the set of “legal transformations” may be expressed; these transformations are the ones which are not considered to be distorting. This flexibility allows us to pose the problems of image resizing and 2D shape deformation in a natural way and generate minimally distorted results. It also allows us to strongly reduce undesirable foldovers or self-intersections. Results of both algorithms demonstrate the effectiveness of our approach.

N. Slesareva, T. Buhler, K. Hagenburg, J. Weickert, A. Bruhn, Z. Karni, H.-P. Seidel, "Robust Variational Reconstruction from Multiple Views", The 15th Scandinavian Conference on Image Analysis, SCIA, 2007.

Recovering a 3-D scene from multiple 2-D views is indispensable for many computer vision applications ranging from free viewpoint video to face recognition. Ideally the recovered depth map should be dense, piecewise smooth with ne level of details, and the recovery procedure shall be robust with respect to outliers and global illumination changes. We present a novel variational approach that satisfies these needs. Our model incorporates robust penalisation in the data term and anisotropic regularisation in the smoothness term. In order to render the data term robust with respect to global illumination changes, a gradient constancy assumption is applied to logarithmically transformed input data. Focussing on translational camera motion and considering small baseline distances between the different camera positions, we reconstruct a common disparity map that allows to track image points throughout the entire sequence. Experiments on synthetic image data demonstrate the favourable performance of our novel method.

C. Stoll, Z. Karni, H.-P. Seidel, "Geodesics Guided Constrained Texture Deformation", The 14th Pacific Conference on Computer Graphics and Applications, Vol 14, pp. 144-152, 2006.

We present a method that deforms an image plane to visually meet the shape and pose of a manifold surface. The user provides constraints that couple a small number of surface points with their corresponding image pixels to initially deform the plane. Matching, based on geodesic distances, couples additional points, followed by a second deformation that brings the image plane into its final pose and shape. The method works on any type of surface that supports geodesic distances evaluation. This includes not-triangulated and high genus models with arbitrary topology. The result is a smooth, visually pleasing and realistic textured surface that can be superimposed onto or used instead of the original model and with some limitations can be considered as a parameterization or remeshing method for the area of interest.

C. Stoll, Z. Karni, C. Rössl, H. Yamauchi,  and H.-P. Seidel, "Template Deformation for Point Cloud Fitting", Symposium on Point-Based Graphics, pp. 27-35, 2006.

The reconstruction of high-quality surface meshes from measured data is a vital stage in digital shape processing. We present a new approach to this problem that deforms a template surface to fit a given point cloud. Our method takes a template mesh and a point cloud as input, the latter typically shows missing parts and measurement noise. The deformation process is initially guided by user specified correspondences between template and data, then during iterative fitting new correspondences are established. This approach is based on a Laplacian setting for the template without need of any additional meshing of the data or cross-parameterization. The reconstructed surface fits to the point cloud while it inherits shape properties and topology of the template. We demonstrate the effectiveness of the approach for several point data sets from different sources.

H. Yamauchi, W. Saleem, S. Yoshizawa, Z. Karni, A. Belyaev and H.-P. Seidel, "Towards Stable and Salient Multi-View Representation of 3D Shapes", Proceedings of the IEEE International Conference on Shape Modeling and Applications (SMI'06), 2006.

An approach to automatically select stable and salient representative views of a given 3D object is proposed. Initially, a set of viewpoints are uniformly sampled along the surface of a bounding sphere. The sampled viewpoints are connected to their closest points to form a spherical graph in which each edge is weighted by a similarity measure between the two views from its incident vertices. Partitions of similar views are obtained using a graph partitioning procedure and their "centroids" are considered to be their representative views. Finally, the views are ranked based on a saliency measure to form the object's representative views. This leads to a compact, human-oriented 2D description of a 3D object, and as such, is useful both for traditional applications like presentation and analysis of 3D shapes, and for emerging ones like indexing and retrieval in large shape repositories.

S. Gumhold, Z. Karni, M. Isenburg and H.-P. Seidel, "Predictive Point-Cloud Compression", Proceedings of the Sixth Israel-Korea Bi-National Conference, pages 125-129, 2005.

Point clouds have recently become a popular alternative to polygonal meshes for representing three-dimensional geometric models. With modern scanning technologies producing larger and larger amounts of point data, it is beneficial to have compact representations for storage and transmission of such data. We present a novel predictive method for single-rate compression of 3D models represented as point-clouds. Our method constructs a prediction tree that specifies which previously encoded points are used for predicting the position of the next point. We use a greedy point-by-point construction of the tree that tries to minimize the prediction error. The results show that our approach can compete with other schemes for compressing point positions. Because our method can be adapted for streaming, out-of-core operation, we can compress arbitrary large point sets using only moderate memory resources.

R. Zayer, C. Rössl, Z. Karni and H.-P. Seidel, "Harmonic Guidance for Surface Deformation", Computer Graphics Forum (Proceedings of Eurographics), Vol 24(3), pages 601-609, 2005.

We present an interactive method for applying deformations to a surface mesh while preserving its global shape and local properties. Two surface editing scenarios are discussed, which conceptually differ in the specification of deformations: Either interpolation constraints are imposed explicitly, e.g., by dragging a subset of vertices, or, deformation of a reference surface is mimicked. The contribution of this paper is a novel approach for interpolation of local deformations over the manifold and for efficiently establishing correspondence to a reference surface from only few pairs of markers. As a general tool for both scenarios, a harmonic field is constructed to guide the interpolation of constraints and to find correspondence required for deformation transfer. We show that our approach fits nicely in a unified mathematical framework, where the same type of linear operator is applied in all phases, and how this approach can be used to create an intuitive and interactive editing tool.

S. Gumhold, Z. Karni, M. Isenburg and H.-P. Seidel, "Predictive Point-Cloud Compression", SIGGRAPH Sketch, 2005.

Point clouds have recently become a popular alternative to polygonal meshes for representing three-dimensional geometric models. 3D photography and scanning systems acquire the geometry and appearance of real-world objects in form of point samples. Rendering directly with points eliminates the complex task of reconstructing a surface and allows handling of non-surfaces like models such as trees. With modern acquisition techniques producing larger and larger amounts of points, efficient schemes for compressing such data have become necessary.

Z. Karni, C. Gotsman and S. J. Gortler "Free-Boundary Linear Parameterization of 3D Meshes in the Presence of Constraints", Proceedings of Shape Modeling International, pages 266-275, 2005.

Linear parameterization of 3D meshes with disk topology is usually performed using the method of barycentric coordinates pioneered by Tutte and Floater. This imposes a convex boundary on the parameterization which can significantly distort the result. Recently, several methods showed how to relax the convex boundary requirement while still using the barycentric coordinates formulation. However, this relaxation can result in other artifacts in the parameterization. In this paper we explore these methods and give a general recipe for “natural” boundary conditions for the family of so-called “three point” barycentric coordinates. We discuss the shortcomings of these methods and show how they may be rectified using an iterative scheme or a carefully crafted "virtual boundary". Finally, we show how these methods adapt easily to solve the problem of constrained parameterization.

Z. Karni and C. Gotsman, "Compression of Soft-Body Animation Sequences", in Computer & Graphics, Special Issue on Compression (28), pages 25-34, 2004.

We describe a compression scheme for the geometry component of 3D animation sequences. This scheme is based on the Principle Component Analysis (PCA) method, which represents the animation sequence using a small number of basis functions. Second order Linear Prediction Coding (LPC) is applied to the PCA coefficients in order to further reduce the code size by exploiting the temporal coherence present in the sequence. Our results show that applying LPC to the PCA scheme results in significant performance improvements relative to other coding methods. Use of these codes will make animated 3D data more accessible for graphics and visualization applications.

Z. Karni, A. Bogomjakov and C. Gotsman, "Efficient Compression and Rendering of Multi-Resolution Meshes", Proceedings of IEEE Visualization, pages 347-354, Boston 2002.

We present a method to code the multiresolution structure of a 3D triangle mesh in a manner that allows progressive decoding and efficient rendering at a client machine. The code is based on a special ordering of the mesh vertices which has good locality and continuity properties, inducing a natural multiresolution structure. This ordering also incorporates information allowing efficient rendering of the mesh at all resolutions using the contemporary vertex buffer mechanism. The performance of our code is shown to be competitive with existing progressive mesh compression methods, while achieving superior rendering speed.

Z. Karni and C. Gotsman, "3D Mesh Compression Using Fixed Spectral Bases", Proceedings of Graphics Interface, Ottawa, pages 1-8, June 2001.

We show how to use fixed bases for efficient spectral compression of 3D meshes. In contrast with compression using variable bases, this permits efficient decoding of the mesh. The coding procedure involves efficient mesh augmentation and generation of a neighborhood-preserving mapping between the vertices of a 3D mesh with arbitrary connectivity and those of a 6-regular mesh.

Z. Karni and C. Gotsman, "Spectral Compression of Mesh Geometry", Computer Graphics (Proceedings of SIGGRAPH), pages. 279-286, 2000.

We show how spectral methods may be applied to 3D mesh data to obtain compact representations. This is achieved by projecting the mesh geometry onto an orthonormal basis derived from the mesh topology. To reduce complexity, the mesh is partitioned into a number of balanced submeshes with minimal interaction, each of which are compressed independently. Our methods may be used for compression and progressive transmission of 3D content, and are shown to be vastly superior to existing methods using spatial techniques, if slight loss can be tolerated.

Z. Karni, D. Orell and S. Ur, "Using 3D to Visualize Dynamic Path Coverage", Proceedings of Quality Week, San Francisco, 1998.

In this paper we illustrate an innovative 3D visualization technique of coverage information and explain its advantages over 2D visualization. We explain how 3D visualization of statement and branch coverage can improve testing. We show, using the forward path coverage criteria, how graphical information can capture dynamic properties of program execution.