1248103
Shape Ambiguities in Structure from Motion
This paper examines the fundamental ambiguities and uncertainties inherent in recovering structure from motion. By examining the eigenvectors associated with null or small eigenvalues of the Hessian matrix, we can quantify the exact nature of these ambiguities and predict how they will affect the accuracy of the reconstructed shape. Our results for orthographic cameras show that the bas-relief ambiguity is significant even with many images, unless a large amount of rotation is present. Similar results for perspective cameras suggest that three or more frames and a large amount of rotation are required for metrically accurate reconstruction.
44673585
Characterization of Errors in Compositing Panoramic Images
A panoramic image has a 360° horizontal field of view, and it can provide the viewer the impression of being immersed in the scene. A panorama is created by first taking a sequence of images while rotating the camera about a vertical axis. These images are then projected onto a cylindrical surface before being seamlessly composited. The cross-sectional circumference of the cylindrical panorama is called thecompositing length. This work characterizes the error in compositing panoramic images due to errors in some of the intrinsic parameters. The intrinsic camera parameters that are considered are the camera focal length and the radial distortion coefficient. We show that the error in the compositing length is more sensitive to the error in the camera focal length. Especially important is the discovery that the relative error in compositing length is always smaller than the relative error in the focal length. This means that the error in focal length can be corrected by iteratively using the composited length to compute a new and more correct focal length. Thiscompositing approach to camera calibrationhas the advantages of not requiring both feature detection and separate prior calibration.
2096181
Video editing using figure tracking and image-based rendering
We describe a new approach to video editing based on the semi-automatic segmentation of video into multiple layers and the composition of layers using image-based rendering. Using figure tracking and background motion estimation, we can segment a moving figure and reconstruct the background. Using geometrically-correct pixel reprojection, layers can be composited on the basis of the geometry of the underlying scene and the position of a virtual camera. We have implemented a prototype editing system called SpliceWorld.
40596005
Survey of image-based representations and compression techniques
We survey the techniques for image-based rendering (IBR) and for compressing image-based representations. Unlike traditional three-dimensional (3-D) computer graphics, in which 3-D geometry of the scene is known, IBR techniques render novel views directly from input images. IBR techniques can be classified into three categories according to how much geometric information is used: rendering without geometry, rendering with implicit geometry (i.e., correspondence), and rendering with explicit geometry (either with approximate or accurate geometry). We discuss the characteristics of these categories and their representative techniques. IBR techniques demonstrate a surprising diverse range in their extent of use of images and geometry in representing 3-D scenes. We explore the issues in trading off the use of images and geometry by revisiting plenoptic-sampling analysis and the notions of view dependency and geometric proxies. Finally, we highlight compression techniques specifically designed for image-based representations. Such compression techniques are important in making IBR techniques practical.
16190492
Noise Estimation from a Single Image
In order to work well, many computer vision algorithms require that their parameters be adjusted according to the image noise level, making it an important quantity to estimate. We show how to estimate an upper bound on the noise level from a single image based on a piecewise smooth image prior model and measured CCD camera response functions. We also learn the space of noise level functions how noise level changes with respect to brightness and use Bayesian MAP inference to infer the noise level function from a single image. We illustrate the utility of this noise estimation for two algorithms: edge detection and featurepreserving smoothing through bilateral filtering. For a variety of different noise levels, we obtain good results for both these algorithms with no user-specified inputs.
47117010
Stylizing 2.5-D video
In recent years considerable interest has been given to non-photorealistic rendering of photographs, video, and 3D models for illustrative or artistic purposes. Conventional 2D inputs such as photographs and video are easy to create and capture, while 3D models allow for a wider variety of stylization techniques, such as cross-hatching. In this paper, we propose using video with depth information (2.5-D video) to combine the advantages of 2D and 3D input. 2.5-D video is becoming increasingly easy to capture, and with the additional depth information, stylization techniques that require shape information can be applied. However, because 2.5-D video contains only limited shape information and 3D correspondence over time is unknown, it is difficult to create temporally coherent stylized animations directly from raw 2.5-D video. In this paper, we present techniques for processing 2.5-D video to overcome these drawbacks, and demonstrate several styles that can be created using these techniques.
53239407
Logic Transformation for Low Power Synthesis
In this paper we present a new approach to the problem of local logic transformation for reduction of power dissipation in logic circuits. Based on the finite-state input transition (FIT) power dissipation model, we introduce a cost function which accounts for the effects of input capacitance, input slew rate, internal parasitic capacitance of logic gates, interconnect capacitance, as well as switching power. Our approach provides an efficient way of estimating estimating the global effect of local logic transformations in logic circuits. In our approach, the FIT model for the transitive fanout cells of a locally transformed subcircuit can be reused to measure the global power dissipation by varying the input probabilities of the transitive fanout cells. Local logic transformation is carried our based on compatible sets of permissible functions (CSPF). Experimental results show that local logic transformation based on CSPF using our cost function can reduce power consumption by about 36% on average without increase in the worst-case circuit delay.
5947702
Fast timing simulation of transient faults in digital circuits
Transient fault simulation is an important verification activity for circuits used in critical applications since such faults account for over 80% of all system failures. This paper presents a timing level transient fault simulator that bridges the gap between electrical and gate-level transient fault simulators. A generic MOS circuit primitive and analytical solutions of node differential equations are used to perform transistor level simulation with accurate MOS-FET models. The transient fault is modeled by a piecewise quadratic injected current waveform; this retains the electrical nature of the transient fault and provides SPICE-like accuracy. Detailed comparisons with SPICE3 show the accuracy of this technique and speedups of two orders of magnitude are observed for circuits containing up to 2000 transistors. Latched error distributions of the benchmark circuits are also provided.
5192887
Convexity-based algorithms for design centering
A new technique for design centering and polytope approximation of the feasible region for a design are presented. In the first phase, the feasible region is approximated by a convex polytope, using a method based on a theorem on convex sets. As a natural consequence of this approach, a good approximation to the design center is obtained. In the next phase, the exact design center is estimated using one of two techniques that we present in this paper. The first inscribes the largest Hessian ellipsoid, which is known to be a good approximation to the shape of the polytope, within the polytope. This represents an improvement over previous methods, such as simplicial approximation, where a hypersphere or a crudely estimated ellipsoid is inscribed within the approximating polytope. However, when the probability density functions of the design parameters are known, the design center does not necessarily correspond to the center of the largest inscribed ellipsoid. Hence, a second technique is developed that incorporates the probability distributions of the parameters, under the assumption that their variation is modeled by Gaussian probability distributions. The problem is formulated as a convex programming problem and an efficient algorithm is used to calculate the design center, using fast and efficient Monte Carlo methods to estimate the yield gradient. An example is provided to illustrate how ellipsoid-based methods fail to incorporate the probability density functions and is solved using the convex programming-based algorithm. >
16084555
2.4GHz ZigBee radio architecture with fast frequency offset cancellation loop
This paper describes a radio architecture with fast analog frequency offset cancellation loop which is based on a SigmaDelta fractional-N frequency synthesizer and a frequency offset detector. The offset detector is composed of a frequency/phase detector (PFD) and a new non-uniform resolution time-to-digital converter (TDC). By adopting the weighted delay-length for the TDC, only 60-DFFs are used to generate digitized timing difference of 250ns with a minimum resolution of 1ns. For the 2.4GHz ZigBee transceiver with 4MHz IF, designed for 0.18mum CMOS process, the frequency offset cancellation time takes about 30mus under the PLL loop-bandwidth of 100 kHz
9442528
Fast and accurate timing simulation with regionwise quadratic models of MOS I-V characteristics
This paper presents a technique called regionwise quadratic (RWQ) modeling that allows highly accurate MOS models, as well as measured I-V data, to be used in fast timing simulation. This technique significantly increases the accuracy of fast timing simulation while maintaining efficiency by permitting analytical solutions of node equations. A fast timing simulator using these RWQ models has been implemented. Several examples of RWQ modeling are provided, and comparisons of simulation results with SPICE3 are shown to demonstrate accuracy and efficiency. Speedups of two to three orders of magnitude for circuits containing up to 2000 transistors are observed.