Karan Singh

University of Toronto, Toronto, Ontario, Canada

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Publications (53)1.23 Total impact

  • Comput. Graph. Forum. 01/2011; 30:613-622.
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    ABSTRACT: Minimalist object representations or shape-proxies that spark and inspire human perception of shape remain an incompletely understood, yet powerful aspect of visual communication. We explore the use of planar sections, i.e., the contours of intersection of planes with a 3D object, for creating shape abstractions, motivated by their popularity in art and engineering. We first perform a user study to show that humans do define consistent and similar planar section proxies for common objects. Interestingly, we observe a strong correlation between user-defined planes and geometric features of objects. Further we show that the problem of finding the minimum set of planes that capture a set of 3D geometric shape features is both NP-hard and not always the proxy a user would pick. Guided by the principles inferred from our user study, we present an algorithm that progressively selects planes to maximize feature coverage, which in turn influence the selection of subsequent planes. The algorithmic framework easily incorporates various shape features, while their relative importance values are computed and validated from the user study data. We use our algorithm to compute planar slices for various objects, validate their utility towards object abstraction using a second user study, and conclude showing the potential applications of the extracted planar slice shape proxies.
    ACM Trans. Graph. 01/2011; 30:168.
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    ABSTRACT: Elasticurves present a novel approach to neaten sketches in real-time, resulting in curves that combine smoothness with user-intended detail. Inspired by natural variations in stroke speed when drawing quickly or with precision, we exploit stroke dynamics to distinguish intentional fine detail from stroke noise. Combining inertia and stroke dynamics, elasticurves can be imagined as the trace of a pen attached to the user by an oscillation-free elastic band. Sketched quickly, the elasticurve spatially lags behind the stroke, smoothing over stroke detail, but catches up and matches the input stroke at slower speeds. Connectors, such as lines or circular-arcs link the evolving elasticurve to the next input point, growing the curve by a responsiveness fraction along the connector. Responsiveness is calibrated, to reflect drawing skill or device noise. Elasticurves are theoretically sound and robust to variations in stroke sampling. Practically, they neaten digital strokes in real-time while retaining the modeless and visceral feel of pen on paper.
    Proceedings of the 24th Annual ACM Symposium on User Interface Software and Technology, Santa Barbara, CA, USA, October 16-19, 2011; 01/2011
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    James McCrae, Karan Singh
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    ABSTRACT: We apply traditional bimanual curve modeling using French curves to the problem of automatic neatening of sketched strokes. Given a sketched input stroke and a set of template French curves we present an approach that fits the stroke using an optimal number of French curve segments. Our algorithm operates in both curvature and point space, reconstructing the salient curvature profiles of French curve segments, while limiting error accumulation resulting from curvature integration. User-controlled parameters allow the neatened stroke to model G2 continuous curves, capture G1 discontinuities, define closed curves and explore the trade-off between fitting error and the number of French curve segments used. We present an interactive sketch stroke neatening implementation to demonstrate the real-time performance of our algorithm and evaluate the quality of its results.
    Sketch Based Interfaces and Modeling, Vancouver, BC, Canada, 5-7 August 2011. Proceedings; 01/2011
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    ABSTRACT: Recently, research in 3D computer graphics and interaction has started to move beyond the narrow domain of single object authoring and inspection, and has begun to consider complex multiscale objects and environments. This generalization of problem scope calls for more general solutions, which are more akin to information visualization techniques than traditional computer graphics approaches. We consider the general problem of the user's understanding of their position and orientation within a multiscale 3D scene and propose a classification of the design space. To ground this theoretical discussion, we present initial explorations into grouping techniques, visualizations, and interactions to facilitate multiscale 3D orientation.
    Proceedings of the International Conference on Advanced Visual Interfaces, AVI 2010, Roma, Italy, May 26-28, 2010; 01/2010
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    ABSTRACT: This paper presents a data-driven approach to simultaneous segmentation and labeling of parts in 3D meshes. An objective function is formulated as a Conditional Random Field model, with terms assessing the consistency of faces with labels, and terms between labels of neighboring faces. The objective function is learned from a collection of labeled training meshes. The algorithm uses hundreds of geometric and contextual label features and learns different types of segmentations for different tasks, without requiring manual parameter tuning. Our algorithm achieves a significant improvement in results over the state-of-the-art when evaluated on the Princeton Segmentation Benchmark, often producing segmentations and labelings comparable to those produced by humans.
    ACM Trans. Graph. 01/2010; 29.
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    Ryan Schmidt, Karan Singh
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    ABSTRACT: In recent years a wide variety of mesh editing techniques have been developed for tasks such as smoothing, deformation, and parameterization. Comparatively fewer alternatives are available for composition tasks, such as combining parts of existing meshes. As designs often evolve from a combination of existing ideas and models, rapid composition techniques could significantly improve the workflow of mesh-based modeling tools. In our work we are exploring shape reuse and composition problems in 3D mesh modeling.
    International Conference on Computer Graphics and Interactive Techniques, SIGGRAPH 2010, Los Angeles, California, USA, July 26-30, 2010, Talks Proceedings; 01/2010
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    ABSTRACT: We present a robust framework for extracting lines of curvature from point clouds. First, we show a novel approach to denoising the input point cloud using robust statistical estimates of surface normal and curvature which automatically rejects outliers and corrects points by energy minimization. Then the lines of curvature are constructed on the point cloud with controllable density. Our approach is applicable to surfaces of arbitrary genus, with or without boundaries, and is statistically robust to noise and outliers while preserving sharp surface features. We show our approach to be effective over a range of synthetic and real-world input datasets with varying amounts of noise and outliers. The extraction of curvature information can benefit many applications in CAD, computer vision and graphics for point cloud shape analysis, recognition and segmentation. Here, we show the possibility of using the lines of curvature for feature-preserving mesh construction directly from noisy point clouds.
    Computer-Aided Design. 01/2009; 41:282-292.
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    Conference Proceeding: Sketch-based path design.
    James McCrae, Karan Singh
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    ABSTRACT: Abstract Sketch-Based Path Design James Palmer McCrae Master of Science Graduate Department of Computer Science University of Toronto 2008 We first present a novel approach to sketching 2D curves with minimally varying cur-
    Proceedings of the Graphics Interface 2009 Conference, May 25-27, 2009, Kelowna, British Columbia, Canada; 01/2009
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    ABSTRACT: A study is described which examines the drawing accuracy of experts when drawing foreshortened projections of 3D curves in ecologically-valid conditions. The main result of this study is that the distribution of error in expert drawings exhibits a bias similar to that previously observed in non-expert subjects, which is dependent on the degree of foreshortening of the imagined drawing surface. A review of existing perceptual studies also finds that only absolute 2D image-space error has been considered, which has been found to be largest with viewing angles of 25--55°. Our visualizations of 3D error indicate that 3D bias continues to increase with decreasing viewing angle. Based on these findings, we analyze current 3D curve drawing techniques for susceptibility to foreshortening bias, and make some suggestions for future sketch-based modeling systems.
    Sketch Based Interfaces and Modeling, New Orleans, Louisiana, USA, 2009. Proceedings; 01/2009
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    Computational Aesthetics 2009: Eurographics Workshop on Computational Aesthetics, Victoria, British Columbia, Canada, 2009; 01/2009
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    ABSTRACT: We describe a novel approach to inferring 3D curves from perspective drawings in an interactive design tool. Our methods are based on a traditional design drawing style known as analytic drawing, which supports precise image-space construction of a linear 3D scaffold. This scaffold in turn acts as a set of visual constraints for sketching 3D curves. We implement analytic drawing techniques in a pure-inference sketching interface which supports both single-and multi-view incremental construction of complex scaffolds and curve networks. A new representation of 3D drawings is proposed, and useful interactive drawing aids are described. Novel techniques are presented for deriving constraints from single-view sketches drawn relative to the current 3D scaffold, and then inferring 3D line and curve geometry which satisfies these constraints. The resulting analytic drawing tool allows 3D drawings to be constructed using exactly the same strokes as one would make on paper.
    ACM Trans. Graph. 01/2009; 28.
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    ABSTRACT: This paper presents a method for real-time line drawing of deforming objects. Object-space line drawing algorithms for many types of curves, including suggestive contours, highlights, ridges and valleys, rely on surface curvature and curvature derivatives. Unfortunately, these curvatures and their derivatives cannot be computed in real-time for animated, deforming objects. In a preprocessing step, our method learns the mapping from a low-dimensional set of animation parameters (e.g., joint angles) to surface curvatures for a deforming 3D mesh. The learned model can then accurately and efficiently predict curvatures and their derivatives, enabling real-time object-space rendering of suggestive contours and other such curves. This represents an order- of-magnitude speed-up over the fastest existing algorithm capable of estimating curvatures and their derivatives accurately enough for many different types of line drawings. The learned model can generalize to novel animation sequences, and is also very compact, typically requiring a few megabytes of storage at run-time. We demonstrate our method for various types of animated objects, including skeleton-based characters, cloth simulation and blend-shape facial animation, using a variety of non-photorealistic rendering styles.
    ACM Trans. Graph. 01/2009; 28.
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    ABSTRACT: We present EverybodyLovesSketch, a gesture-based 3D curve sketching system for rapid ideation and visualization of 3D forms, aimed at a broad audience. We first analyze traditional perspective drawing in professional practice. We then design a system built upon the paradigm of ILoveS- ketch, a 3D curve drawing system for design professionals. The new system incorporates many interaction aspects of perspective drawing with judicious automation to enable novices with no perspective training to proficiently create 3D curve sketches. EverybodyLovesSketch supports a number of novel interactions: tick-based sketch plane se- lection, single view definition of arbitrary extrusion vectors, multiple extruded surface sketching, copy-and-project of 3D curves, freeform surface sketching, and an interactive perspective grid. Finally, we present a study involving 49 high school students (with no formal artistic training) who each learned and used the system over 11 days, which pro- vides detailed insights into the popularity, power and us- ability of the various techniques, and shows our system to be easily learnt and effectively used, with broad appeal.
    Proceedings of the 22nd Annual ACM Symposium on User Interface Software and Technology, Victoria, BC, Canada, October 4-7, 2009; 01/2009
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    James McCrae, Karan Singh
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    ABSTRACT: We present a novel approach to sketching 2D curves with minimally varying curvature as piecewise clothoids. A stable and efficient algorithm fits a sketched piecewise linear curve using a number of clothoid segments with G2 continuity based on a specified error tolerance. Further, adjacent clothoid segments can be locally blended to result in a G3 curve with curvature that predominantly varies linearly with arc length. We also handle intended sharp corners or G1 discontinuities, as independent rotations of clothoid pieces. Our formulation is ideally suited to conceptual design applications where aesthetic fairness of the sketched curve takes precedence over the precise interpolation of geometric constraints. We show the effectiveness of our results within a system for sketch-based road and robot-vehicle path design, where clothoids are already widely used.
    Sketch Based Interfaces and Modeling, Annecy, France, 2008. Proceedings; 01/2008
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    ABSTRACT: We present ILoveSketch, a 3D curve sketching system that captures some of the affordances of pen and paper for pro- fessional designers, allowing them to iterate directly on concept 3D curve models. The system coherently integrates existing techniques of sketch-based interaction with a num- ber of novel and enhanced features. Novel contributions of the system include automatic view rotation to improve curve sketchability, an axis widget for sketch surface selec- tion, and implicitly inferred changes between sketching techniques. We also improve on a number of existing ideas such as a virtual sketchbook, simplified 2D and 3D view navigation, multi-stroke NURBS curve creation, and a co- hesive gesture vocabulary. An evaluation by a professional designer shows the potential of our system for deployment within a real design process.
    Proceedings of the 21st Annual ACM Symposium on User Interface Software and Technology, Monterey, CA, USA, October 19-22, 2008; 01/2008
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    Comput. Graph. Forum. 01/2008; 27:301-310.
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    ABSTRACT: We introduce staggered poses---a representation of character motion that explicitly encodes coordinated timing among movement features in different parts of a character's body. This representation allows us to provide sparse, pose--based controls for editing motion that preserve existing movement detail, and we describe how to edit coordinated timing among extrema in these controls for stylistic editing. The staggered pose representation supports the editing of new motion by generalizing keyframe--based workflows to retain high--level control after local timing and transition splines have been created. For densely--sampled motion such as motion capture data, we present an algorithm that creates a staggered pose representation by locating coordinated movement features and modeling motion detail using splines and displacement maps. These techniques, taken together, enable feature--based keyframe editing of dense motion data.
    Proceedings of the 2008 Eurographics/ACM SIGGRAPH Symposium on Computer Animation, SCA 2008, Dublin, Ireland, 2008; 01/2008
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    ABSTRACT: We present a method for browsing videos by directly drag- ging their content. This method brings the benefits of direct manipulation to an activity typically mediated by widgets. We support this new type of interactivity by: 1) automati- cally extracting motion data from videos; and 2) a new technique called relative flow dragging that lets users con- trol video playback by moving objects of interest along their visual trajectory. We show that this method can out- perform the traditional seeker bar in video browsing tasks that focus on visual content rather than time.
    Proceedings of the 2008 Conference on Human Factors in Computing Systems, CHI 2008, 2008, Florence, Italy, April 5-10, 2008; 01/2008
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    Ryan Schmidt, Karan Singh
    Comput. Graph. Forum. 01/2008; 27:321-330.