10850316
Modeling realistic virtual hairstyles
The author presents an effective method for modeling realistic curly hairstyles, taking into account both artificial hairstyling processes and natural curliness. The result is a detailed geometric model of hairs that can be rendered and animated via existing methods. Our technique exploits the analogy between hairs and a vector field; it interactively and efficiently models global and local hair flows by superimposing procedurally defined vector field primitives that have local influence. Usually only a very small number of vector field primitives are needed to model a complicated hairstyle. An initial model of hair strands is extracted from the superimposed vector fields by tracing their field lines. Random natural or artificial curliness can be added to the initial model through a parametric hair offset function with a randomized distribution of parameters over the scalp. Techniques for shearing and clustering are also designed to improve the overall appearance of the hair model. Our technique has been successfully applied to generate a variety of realistic hairstyles with different curliness and length distributions.
11797790
Two-Level Image Segmentation Based on Region and Edge Integration
This paper introduces a two-level approach for image seg- mentation based on region and edge integration. Edges are first detected in the original image using a combination of operators for intensity gra- dient and texture discontinuities. To preserve the spatial coherence of the edges and their surrounding image regions, the detected edges are vectorized into connected line segments which serve as the basis for a constrained Delaunay triangulation. Segmentation is first performed on the triangulation using graph cuts. Our method favors segmentations that pass through more vectorized line segments. Finally, the obtained segmentation on the triangulation is projected onto the original image and region boundaries are refined to achieve pixel accuracy. Experimen- tal results show that the two-level approach can achieve accurate edge localization, better spatial coherence and improved efficiency.
1372639
Motion Field Estimation for Temporal Textures
This paper presents a novel approach for estimating the flow fields of dynamic temporal textures whose motion differs radically from that of rigid bod- ies. Our approach is based on a local flow probability distribution function at each pixel using the STAR model and the data from a spatio-temporal neighborhood. The peak of this density function can be regarded as the estimated local flow vec- tor. Our complete algorithm exploits a two-stage process. The first stage of the algorithm applies a simple tensor method to estimate the direction of the optical flow at each pixel in the texture. In the second stage, the flow probability function is used to perform a one-dimensional search along the flow direction to obtain the magnitude. Performance analysis and experiments with real video sequences show that our methods can successfully estimate flow fields.
1542177
Out-of-core tensor approximation of multi-dimensional matrices of visual data
Tensor approximation is necessary to obtain compact multilinear models for multi-dimensional visual datasets. Traditionally, each multi-dimensional data item is represented as a vector. Such a scheme flattens the data and partially destroys the internal structures established throughout the multiple dimensions. In this paper, we retain the original dimensionality of the data items to more effectively exploit existing spatial redundancy and allow more efficient computation. Since the size of visual datasets can easily exceed the memory capacity of a single machine, we also present an out-of-core algorithm for higher-order tensor approximation. The basic idea is to partition a tensor into smaller blocks and perform tensor-related operations blockwise. We have successfully applied our techniques to three graphics-related data-driven models, including 6D bidirectional texture functions, 7D dynamic BTFs and 4D volume simulation sequences. Experimental results indicate that our techniques can not only process out-of-core data, but also achieve higher compression ratios and quality than previous methods.
123116880
Shadow Graphs and 3D Texture Reconstruction
We present methods for recovering surface height fields such as geometric details of 3D textures by incorporating shadow constraints. We introduce shadow graphs which give a new graph-based representation for shadow constraints. It can be shown that the shadow graph alone is sufficient to solve the shape-from-shadow problem from a dense set of images. Shadow graphs provide a simpler and more systematic approach to represent and integrate shadow constraints from multiple images. To recover height fields from a sparse set of images, we propose a method for integrated shadow and shading constraints. Previous shape-from-shadow algorithms do not consider shading constraints while shape-from-shading usually assumes there is no shadow. Our method is based on collecting a set of images from a fixed viewpoint as a known light source changes its position. It first builds a shadow graph from shadow constraints from which an upper bound for each pixel can be derived if the height values of a small number of pixels are initialized correctly. Finally, a constrained optimization procedure is designed to make the results from shape-from-shading consistent with the height bounds derived from the shadow constraints. Our technique is demonstrated on both synthetic and real imagery.
46180
Efficient visibility processing for projective texture mapping
Abstract Projective texture mapping is a powerful tool for image-based rendering. However, visibility information must be obtained in order to project correct textures onto the geometric sturcture. This paper presents a novel visibility algorithm for determining which polygons are visible from each camera position. It has object-space precision, but operates in both image-space and object-space to get better performance. It generates much less polygons than traditional object-space algorithms to help accelerate the speed of texture mapping. The techniques used to achieve these are conservative image-space occlusion testing and object-space shallow clipping . This algorithm has been successfully used to generate large-scale image-based rendering of a whole university campus, and image-based rendering of architectures under dynamic lighting.
15594560
FRM-Based FIR Filters with Minimum Coefficient Sensitivities
A method for optimizing FRM-based FIR filters with optimum coefficient sensitivity is presented. This technique can be used in conjunction with nonlinear optimization techniques to design very sharp filters that do not only have very sparse coefficient values but also very low coefficient sensitivity.
1769883
FRM based FIR filter design - the WLS approach
Frequency-response masking (FRM) technique produces a filter network which comprises several sub-filters with very sparse coefficient values. If the sub-filters are optimized separately, the overall filter network will be suboptimal. In this paper, an unconstrained weighted least squares algorithm for simultaneously optimizing the sub-filters generated by the frequency-response masking technique is presented. Simulation runs show that our proposed technique produces significant reduction in the effective filter length.
14253908
Proactive vs reactive approaches to failure resilient routing
Dealing with network failures effectively is a major operational challenge for Internet service providers. Commonly deployed link state routing protocols such as OSPF react to link failures through global (i.e., network-wide) link state advertisements and routing table recomputations, causing significant forwarding discontinuity after a failure. The drawback with these protocols is that they need to trade off routing stability and forwarding continuity. To improve failure resiliency without jeopardizing routing stability, we propose a proactive local rerouting based approach called failure insensitive routing (FIR). The proposed approach prepares for failures using interface-specific forwarding, and upon a failure, suppresses the link state advertisement and instead triggers local rerouting using a backwarding table. In this paper, we prove that when no more than one link failure notification is suppressed, FIR always finds a loop-free path to a destination if one such path exists. We also formally analyze routing stability and network availability under both proactive and reactive approaches, and show that FIR provides better stability and availability than OSPF.
26872843
Promoting the use of information technology in education via lightweight authoring tools
The potential benefits of using information technology in classrooms for enhancing students' learning have been well known, but the realisation of these benefits is often hindered by a number of factors, notably the lack of knowledge/skills of teachers, the lack of appropriate software, insufficient teacher time, and the limitation of hardware and network infrastructure. In this paper, we introduce the approach of using lightweight authoring tools to address the difficulties faced by teachers. This approach has been adopted on many occasions for the continuing development of primary school teachers in Hong Kong, including many workshops and a formal in-service teacher education course. This paper describes how the approach works, and reports our experiences and the very encouraging feedback we received with the use of lightweight authoring tools.
7801331
FPGA implementation of digital filters synthesized using the frequency-response masking technique
The effective length of a filter designed using the frequency-response masking technique is very high and requires a very large number of delay elements. In this paper, we present some useful techniques for reducing the data transfer between the FPGA and external memory when the random logic are implemented using FPGA and the delay elements are implemented using external memory such as DRAM.