G. de Jager

A survey of point pattern matching techniques and a new approach to point pattern recognition

The new technique developed by the authors is invariant to rotational, scaling and translational transformations, and is optionally reflection invariant. The techniques presented are compared, and specific applications described.<<ETX>>

A technique for automatically segmenting images of the surface froth structures that are prevalent in industrial flotation cells

The froth structures convey considerable visual information on cell performance, particularly in terms of grade and recovery. Fundamental to the design of a machine vision system for monitoring the operation is the ability to identify and extract those visual features that are descriptive of the surface froth. The individual bubbles give rise to complex 3-dimensional structures that are problematic to segment accurately and reliably. This paper briefly discusses the classical segmentation of surface froth images and then presents a morphological image processing technique that is capable of segmenting surface froth images accurately and reliably.<<ETX>>

The measurement of signal to noise ratio of a television broadcast picture

The authors present a method by which an estimate of the signal-to-noise ratio of a television broadcast picture can be made using excursions from the mean signal level in both the horizontal and vertical directions. The method depends on a determination of the two-dimensional spectral components of the noise and can yield nonintrusive measurements during normal broadcasts. In addition, the method can be used on pictures with no areas of constant luminance. The results obtained are consistent with those produced by an industry standard instrument. >

Rock recognition using feature classification

A knowledge based approach to finding fixed size rocks within an image is described. It is intended to be a building block within a multiresolution system. Each point is hypothesised to be a rock and a region surrounding it is labelled using knowledge of rock characteristics. Twelve features are then measured and used to test the hypothesis by means of a combination of thresholding and k-nearest-neighbour classification.

Uniformly most powerful cyclic permutation invariant detection for discrete-time signals

The uniformly most powerful invariant (UMPI) test is derived for detecting a target with unknown location in a noise sequence. This test has the property that for each possible target location it has the greatest power of all tests which are invariant to cyclic permutations of the observations. The test is compared to the generalised likelihood ratio test (GLRT), which is commonly used as a solution to this detection problem. Monte-Carlo simulations show that the powers of the two tests are comparable, thereby justifying near-optimality of the GLRT.

On the reduction of fractal image compression encoding time

Lossy image coding by partitioned iterated function systems, popularly known as fractal image compression, has recently become an active area of research. An image is coded as a set of contractive transformations in a complete metric space. As a result of a well known theorem in metric space theory, the set of contractive transformations (subject to a few constraints) is guaranteed to produce an approximation to the original image, when iteratively applied to any initial image. While rapid decompression algorithms exist, the compression process is extremely time consuming; an exhaustive search for the optimum mappings is O(n/sup 4/) for an n/spl times/n image. The most common solution involves classification of domain and range blocks according to features such as the presence of edges, after which matches across class boundaries are excluded. We propose a geometric construction, allowing clustering, as well as providing upper and lower bounds for the best match between domain and range blocks, allowing blocks to be excluded from the computationally costly matching process.

Use of a general imaging model to achieve predictive autofocus in the scanning electron microscope

Abstract This work outlines the development of a general imaging model for use in autofocus, astigmatism correction, and resolution analysis. The model is based on the modulation transfer function of the system in the presence of aberrations, in particular, defocus. The signals used are related to the ratios of the Fourier transforms of images captured under different operating conditions. Methods are developed for working with these signals in a consistent manner. The model described is then applied to the problem of autofocus. A fairly general autofocus algorithm is presented and results given which reflect the predictive properties of this model. The imaging system used for the generation of results was a scanning electron microscope (SEM), although the conclusions should be valid across a far wider range of instruments. It is, however, the specific requirements of the SEM that make the generalisation presented here particularly useful. We have, therefore, confined our investigation to SEM.

An approach to rock size measurement based on a model of the human visual system

Abstract This paper describes research into the development of an instrument for the purpose of performing online measurement of rock size distributions using machine vision. Such an instrument would have application in the gold mining industry where it could be used to measure the fragmentation of gold ore on a conveyor belt feed to an autogenous mill, for the purpose of controlling the mill. A computation structure has been developed to identify and delineate rocks in an image for the purpose of measuring their areas. It is based on the human visual system in that it consists of a low-level preattentive vision stage and a higher-level stage of attention focusing. Multiscalar image processing techniques have also been integrated in order to improve the detection of rocks across a wide range of sizes. A performance advantage can be obtained in this way because all the algorithms can be better matched to the size of objects being detected.

RRB-SIMD: RTP Rate-Based SIMD Protocol for Media Streaming Applications over the Internet

Congestion control is vital in the streaming of a video sequence or clip, as network traffic varies unpredictably requiring constant adjustment of the transmission rate. Standard TCP-Friendly Rate Control (TFRC) wastes bandwidth and may react to congestion only when packet loss has already occurred. This paper presents a unicast transport protocol named RRB-SIMD for video streaming over the Internet, that provides better quality of service (QoS) support than the TCP-friendly rate control. RRB-SIMD operates on top of Real-time Transport Protocol (RTP) and takes advantage of Real-time Transport Control Protocol (RTCP) reports to multiplicatively decrease the transmission rate in response to congestion and quadratically increase the transmission rate in the absence of congestion. Since packet loss is not a reliable indicator of congestion, RB-SIMD uses in addition the cumulative jitter as a control criterion to detect incipient congestion prior to loss of a packet. The cumulative jitter scheme is reinforced with a delay factor that measures on a per round basis the buffer occupancy at the bottleneck path between the sender and the receiver. This is done to reduce the risk of unnecessary decrease of the transmission rate every time that incipient congestion is reported through the cumulative jitter scheme. The performance evaluation results using both network-related metrics and video quality measurement shows that RRB-SIMD exhibits a better performance with respect to lost frames ratio, delay and cumulative jitter, and hence an improved quality display than the standard TFRC.

Round-trip time estimation in telecommunication networks using composite expanding and fading memory polynomials

Heterogeneous communication networks with their variety of application demands, time-varying load, and mixture of wired and wireless links pose several challenging problems in modeling and control. This paper focuses on estimation of the round trip time which is important for the transport layer because it impacts the throughput of TCP and allows efficient development of congestion control techniques for multimedia applications. An algorithm that combines expanding and fading memory polynomials to predict a future value of the round trip time from previously recorded values is proposed. Comparison using real data collected when streaming a video over the Internet proves that a composite filter of degree zero provides better start-up estimations than the round trip time estimator currently used in TCP. Additionally, the paper provides an algorithm of a composite polynomial filter of degree 3 and illustrates its ability in tracking the instant value of the round trip time.