Roger A. Packwood

Quadtree-structured variable-size block-matching motion estimation with minimal error

This paper reports two efficient quadtree-based algorithms for variable-size block matching (VSBM) motion estimation. The schemes allow the dimensions of blocks to adapt to local activity within the image, and the total number of blocks in any frame can be varied while still accurately representing true motion. This permits adaptive bit allocation between the representation of displacement and residual data, and also the variation of the overall bit-rate on a frame-by-frame basis. The first algorithm computes the optimal selection of variable-sized blocks to provide the best-achievable prediction error under the fixed number of blocks for a quadtree-based VSBM technique. The algorithm employs an efficient dynamic programming technique utilizing the special structure of a quadtree. Although this algorithm is computationally intensive, it does provide a yardstick by which the performance of other more practical VSBM techniques can be measured. The second algorithm adopts a heuristic way to select variable-sized square blocks. It relies more on local motion information than on global error optimization. Experiments suggest that the effective use of local information contributes to minimizing the overall error. The result is a more computationally efficient VSBM technique than the optimal algorithm, but with a comparable prediction error.

A hierarchical multiple-SIMD architecture for image analysis

Real-time image analysis requires the use of massively parallel machines. Conventional parallel machines consist of an array of identical processors organized in either single instruction multiple data (SIMD) or multiple instruction multiple data (MIMD) configurations. Machines of this type generally only operate effectively on parts of the image analysis problem. SIMD on the low level processing and MIMD on the high level processing. In this paper we describe the Warwick Pyramid Machine, an architecture consisting of both SIMD and MIMD parts in a multiple-SIMD (MSIMD) organization which can operate effectively at all levels of the image analysis problem.

Performance evaluation of the hierarchical Hough transform on an associative M-SIMD architecture

The application of multiple-single instruction multiple-data (M-SIMD) processing techniques to the problem of finding straight lines in an image is described, and the advantages of using these techniques instead of direct SIMD computation are illustrated by reference to a hierarchical architecture: the Warwick pyramid machine. The advantages over conventional implementations of the Hough transform are discussed, and performance timings for a hierarchical implementation are provided.<<ETX>>

Detection and segmentation of blobs using the Warwick multiple-SIMD architecture

The Warwick Pyramid Machine (WPM) is an M-SIMD (Multiple-Single Instruction Multiple Data) heterogeneous pyramid architecture for image understanding. Details of the implementation are given. The properties and performance of the architecture are discussed. A generic image analysis task is the detection and identification of compact, convex, blob-like objects. The detection of such blobs is illustrated in detail with a modification of the circle Hough transform. This is shown to suit the global SIMD nature of the architecture. The subsequent stage of segmentation demonstrates the local processing capabilities of the M-SIMD architecture. The image analysis examples reported use forward-looking infrared images of vehicles, and electron micrographs of virus particles. In both cases the aim is to detect candidate regions of the image for further detailed analysis.

Efficient Motion Estimation and Coding for Arbitrary-Shaped Video Objects

We extend quad-tree-structured variable size block matching (VSBM) techniques for the estimation of motion in arbitrary-shaped video objects. Coding efficiency is significantly improved over recently developed object-based coding schemes that employ fixed size block matching (FSBM). Evaluation on MPEG-4 video object test sequences show that inherent motion is represented by considerably fewer blocks for similar prediction quality. Motion vectors are differentially encoded using a 2-D predictor, and further coding efficiencies are gained by exploiting the spatial redundancy of vector information. VSBM is extended to exploit areas of uniform motion within video objects. This modified VSBM (MVSBM) technique is shown to outperform both FSBM and VSBM for small objects with a high degree of disparate motion. Finally, a technique that minimizes temporal redundancies for the VSBM and MVSBM data structures is presented. Overall savings of up to 21% are achieved in coding the motion information, including tree descriptions and other overheads.