Krasimir D. Kolarov

The haptic display of complex graphical environments

Force feedback coupled with visual display allows people to interact intuitiv ely with complex virtual environments. For this synergy of haptics and graphics to flourish, however, haptic systems must be capable of modeling environments with the same richness, complexity and interactivity that can be found in existing graphic systems. To help meet this challenge, we have developed a haptic rendering system that allows for the efficient tactile display of graphical information. The system uses a common high-level framework to model contact constraints, surface shading, friction and tex ture. The multilevel control system also helps ensure that the haptic device will remain stable even as the limits of the renderer’s capabilities are reached.

Low cost video compression using fast, modified Z-coding of wavelet pyramids

This paper describes a fast, low-complexity, entropy efficient video coder for wavelet pyramids. This coder approaches the entropy-limited coding rate of video wavelet pyramids, is fast in both hardware and software implementations, and has low complexity (no multiplies) for use in ASICs. It consists of a modified Z-coder used to code the zero/non-zero significance function and Huffman coding for the non-zero coefficients themselves. Adaptation is not required. There is a strong speed-memory trade-off for the Huffman tables allowing the coder to be customized to a variety of platform parameters.

Landscape ruggedness in evolutionary algorithms

The paper describes a model for the exploration of the dynamics of interaction in a population of individuals using an evolutionary approach. In particular we analyze the effect of the complexity of the fitness landscape and the population size on the performance of an evolutionary algorithm in terms of speed of fixation and fixation to sub optimal individuals. Our evolutionary model resembles those in the field of population genetics and approaches evolution as a process of adaptation rather than an optimization, The simulation results from our experiments are justified with a theoretical probabilistic analysis of the dynamics of the population with and without recombination. The paper introduces several new insights into the interaction and roles of the different parameters of an evolutionary system. There have been very few attempts to theoretically analyze the dynamics of interaction between the different operators and the performance of GA. We give a detailed description of our model. The experiment for which we vary the ruggedness of the landscape is described. To better understand the results presented, we perform a theoretical analysis of the model and derive recursive formulas describing the dynamics of interaction in the model. These results are explained and some conclusions are drawn.

On the number of links and placement of telescoping manipulators in an environment with obstacles

The authors consider the following problem: Given an environment with obstacles, what are the minimum number of telescoping links that will allow a manipulator operating in this environment to reach every point in the environment. A geometrical algorithm is presented for solving this problem in a two-dimensional planar case when the obstacles are polygonal. Solutions to some generalizations of this problem are outlined, including simultaneous design of a manipulator and its environment, design of a moving robot and/or obstacles, and design for a three-dimensional workspace. Some theorems on the bounding limits for the number of links of the manipulator are formulated.<<ETX>>

Wavelet compression for 3D and higher-dimensional objects

We present a technique to compress scalar functions defined on 2-manifolds of arbitrary topology. Our approach combines discrete wavelet transforms with zerotree compression, building on ideas from three previous developments: the lifting scheme, spherical wavelets, and embedded zerotree coding methods. Applications lie in the efficient storage and rapid transmission of complex data sets. Typical data sets are earth topography, satellite images, and surface parameterizations. Our contribution in this paper is the novel combination and application of these techniques to general 2-manifolds.

Best estimates for the construction of robots in environments with obstacles

The authors consider the design of robots that work in environments with obstacles. The environment and the obstacles are fixed and the robot consists of telescoping links with two degrees of freedom each, one revolute and one prismatic. The objective is to estimate the lowest number of telescoping links that the robot should have so that it can reach all the points in the workspace that are not inside the obstacles. Several estimates are derived for the planar case using different polygonal shapes for the obstacles and the outside boundary of the environment. An algorithm for finding a suboptimal estimate for the number of links in the plane is outlined. Some results for the three-dimensional case with polyhedral obstacles are obtained.<<ETX>>

Optimization of the SW algorithm for high-dimensional compression

This paper describes an algorithm and a software package SW (Spherical Wavelets) that implements a method for compression of scalar functions defined on 3D objects. This method combines discrete second generation wavelet transforms with an extension of the embedded zerotree coding method. We present some results on optimizing the performance of the SW algorithm via the use of arithmetic coding, different scaling and norms of the wavelet coefficients. We describe an extension of the SW algorithm using different prediction schemes in the zerotree mechanism. The combined use of those techniques leads to a significant improvement of the compression performance of SW.

Very low cost video wavelet codec

This paper describes a motion Wavelet transform Zero Tree (WZT) codec which achieves good compression ratios and can be implemented in a single ASIC of modest size (and very low cost). WZT includes a number of trade-offs which reduce the compression rate but which simplify the implementation and reduce the cost. The figure of merit in our codec is ASIC silicon area required, and we are willing to sacrifice some rate/distortion performance with respect to the best available algorithms to that goal. The codec employs a group of pictures (GOP) of two interlaced video frames (i.e., four video fields). Each such field is coded by the well-known transform method, whereby the image is subjected to a 2-D linear transform, the transform values are quantized, and the resulting values coded (e.g., by a zero-tree method). To that goal we are using 3D wavelet transform, dyadic quantization and various entropy codecs. In the temporal direction a temporal transform is used instead of motion estimation. Some of the technical innovations that enable the above features set are: (1) Edge filters which enable blockwise processing while preserving quadratic continuity across block boundaries, greatly reducing blocking artifacts. (2) Field image compression which reduces memory requirements for fields within a GOP.

A fractional chip wavelet zero tree codec (WZT) for video compression

[Summary form only given]. We introduce a motion wavelet transform zero tree (WZT) codec which achieves good compression ratios and can be implemented in a single ASIC of modest size. The codec employs a group of pictures (GOP) of two interlaced video frames, edge filters for the boundaries, intermediate field image compression and block compression structure. Specific features of the implementation for a small single chip are: 1) Transform filters are short and use dyadic rational coefficients with small numerators. Implementation can be accomplished with adds and shifts. We propose a Mallat pyramid resulting from five filter applications in the horizontal direction and three applications in the vertical direction. We use modified edge filters near block and image boundaries so as to utilize actual image values. 2) Motion image compression is used in place of motion compensation. We have applied transform compression in the temporal direction to a GOP of four fields. A two level temporal Mallat pyramid is used as a tensor product with the spatial pyramid. The linear edge filters are used at the fine level and the modified Haar filters at the coarse level, resulting in four temporal subbands. 3) Processing can be decoupled into the processing of blocks of 8 scan lines of 32 pixels each. This helps reduce the RAM requirements to the point that the RAM can be placed in the ASIC itself. 4) Quantization denominators are powers of two, enabling implementation by shifts. 5) Zero-tree coding yields a progressive encoding which is easily rate controlled. 6) The codec itself imposes a very low delay of less than 3.5 ms within a field and 67 ms for a GOP. The overall conclusion is that it is reasonable to expect that this method can be implemented, including memory, in a few mm/sup 2/ of silicon.

Fast, modified Z-coding of wavelet pyramids

[Summary form only given]. This paper describes a fast, low-complexity, entropy efficient coder for wavelet pyramids. This coder approaches the entropy-limited coding rate of video wavelet pyramids, is fast in both hardware and software implementations, and has low complexity for use in ASICs. It consists of a modified Z-coder used to code the zero/non-zero significance function without adaptation. The wavelet pyramid is further sharpened by scaling to match the characteristics of the human visual system (HVS). We derive the statistical characteristics of quantized wavelet pyramids from NTSC video viewed under standard conditions. These video pyramids have substantial runs of zeros and also substantial runs of non-zeros. To explore these we developed a modification of the Z-coder and explored an application of it to code zero versus non-zero. Z-codecs have the advantage of a simple (no multipliers) and fast implementation combined with coding performance approximating that of an arithmetic codec. Our experiments showed that this coder compares favorably with straight arithmetic coding. Our encoder has significant speed advantage due to low cost implementation.