摘要:

The value of image contours in three important areas of image processing and analysis is illustrated. The three areas are those of image compression, shape recognition and stereopsis. The compression ratios of classical image coding techniques such as linear prediction and transform coding appear to have reached a saturation level of around 10:1. It is a widely accepted view that radical new coding schemes must be developed if the real-time transmission of digital images is to be achieved. Contours have been used for many years in cartography, where a sparse set of smooth connected curves convey a very accurate impression of the landscape. A method is outlined of storing digital images in terms of their constant intensity contours. As the images are stored directly in terms of the shapes contained within them it is possible to carry out both object recognition and stereopsis using the compressed form of the image. Examples of compression, shape recognition and stereo matching based on contours are presented.

DOI:10.1049/ip-i-2.1992.0001

出版商:IEE    

年代:1992

数据来源: IET

摘要:

In the encoding of image sequences for transmission and storage, the coding algorithm must have the ability to adapt to changing image characteristics from sequence to sequence and from frame to frame. A new adaptive treestructured vector quantisation (adaptive TSVQ) with multipath searching is described. The structure of the codebook tree is reorganised at an update interval, without requiring any transmission of side information. The 1-path tree searching algorithm is a simple method of finding the closest codeword in TSVQ. The disadvantage of 1-path searching is that the selected codewords are not, in general, closest to the input vectors. Hence, the multipath searching algorithm is proposed to improve the image quality. The improvement over the fixed TSVQ at the same bit rate is up to 2.54 dB when the number of the leaves in the codebook tree is 256 and 4-path searching is applied.

DOI:10.1049/ip-i-2.1992.0002

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Most early communication satellite systems are power-limited; as improvements are made on launch vehicles and satellites become larger, the tendency has shifted from powerlimited to bandwidth-limited systems. In bandlimited nonlinear satellite applications, various papers have shown that respectable coding gains can be achieved by Ungerboeck TCM (trellis code modulation) codes, making them popular in this application owing to the advantage of performance improvement without bandwidth increase or transmitter power increase, and with the codes displaying their robustness to the nonlinearity and band-limiting that prevail in satellite channels. A recent paper by Viterbi proposed pragmatic codes which have a single coder and decoder for various bandwidth efficiencies and achieve a performance comparable to that of Ungerboeck codes on a linear Gaussian channel. These codes are punctured versions of the basic 1/2 rate convolutional code mapped into MPSK signal phase constellation. In this paper, the performance on band-limited nonlinear satellite channel of pragmatic 8PSK codes is studied with respect to equivalent Ungerboeck 8PSK codes. Computer simulation is used to estimate the coding gains achieved on these various codes, and lower bounds for bit error probability are estimated through formulas approximated by Forney. Signal space diagrams are also plotted to show the band-limiting effect, giving a better picture of the signal point dispersion phenomenon caused by severe band-limitation of the satellite channel.

DOI:10.1049/ip-i-2.1992.0003

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A representation of the Kerdock codeK(m)is given that allows instantaneous encoding and the use of different complete decoding strategies. Applications to error correction and to vector quantisation are described. The particularly interesting codeK(4)is thoroughly analysed and the associated bit-error rate on the binary symmetric channel is derived in closed form.

DOI:10.1049/ip-i-2.1992.0004

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Several different sequences for frame synchronisation have been published in the literature. Recently, even sequences using complex signal alphabets have been specified. Whether binary or complex, they are always chosen according to the properties of their autocorrelation function. However, the probability of being out of synchronisation has not as such been considered sufficiently. The paper serves as a compendium of derivations of such probability formulas for various applications and conditions, including both binary and complex signal constellations. Hard quantisation as well as the continuous case are treated.

DOI:10.1049/ip-i-2.1992.0005

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper provides a technique to design and approximate computationally efficient digital filter banks whose centre frequencies are spaced logarithmically. The design procedure consists of two steps: The design of ‘mother’ filter banks and the frequency windowing processing for the final filter banks. The resonator with the purely imaginary transfer function on the unit circle is treated as the basic element of the mother bank and the frequency interpolating filter bank structure is applied. Different pole-zero structures are studied and an infinite filter bank is explored from the theoretical point of view. The outputs of the mother filter banks are weighted and summed to produce the final banks with significantly improved responses. Linear programming is applied to find the optimal weighting coefficients, and the experiments for a variety of windows are made with a discussion of the results and some tradeoffs for window selection. The results show that these filter banks have good frequency response and allow control of crossover gain, and they are useful for voice and music analysis and tone receivers.

DOI:10.1049/ip-i-2.1992.0006

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A fast zero tracking algorithm for resolving coherent sources in power inversion adaptive arrays is investigated. To resolveMdirectional sources with a maximum coherent group size ofMa, the originalM+ 1 element power inversion array is augmented byMa− 1 elements to result in a total ofMaidentical but spatially shiftedM+ 1 element arrays. After performing some simple preprocessing, theMcontrolling zeros in theseMaarrays are adaptively updated in a time-multiplexed manner by using the LMS algorithm to minimise the spatially averaged output power to track the external environment. Since only one zero is adjusted at any instant, the new algorithm has almost the same implementation complexity as when the LMS algorithm is used directly. However, rather than having to use a root-finding routine, the directions of the sources can be obtained directly from the zeros being updated in the new algorithm. Also, with the same asymptotic time constant for all the zeros, the new algorithm can be much faster than the conventional LMS algorithm, especially under situations where the eigenvalue spread of the element covariance matrix is large.

DOI:10.1049/ip-i-2.1992.0007

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Application of the exponential power estimation (EPE) technique to develop computationally simple algorithms for adapting the quantiser and predictor of an adaptive differential pulse code modulation (ADPCM) system has been investigated. Performance of this EPE-based ADPCM system (E-ADPCM) has been studied for first order Gauss-Markov and real speech inputs (three sentences) under different channel conditions (noise-free and noisy channels), using a Gaussian non-uniform quantiser at the bit-rate of 16 kilobits per second (kbit/s). Performance of the proposed ADPCM has been compared with that of two conventional ADPCM systems. The E-ADPCM has a superior performance to the conventional systems considered, with a computational advantage of (3N+ B + 1) multiplications (Nbeing the predictor order andB, the number of bits per sample used for quantising the prediction error) and one division per iteration compared with the first system and (B+ 1) multiplications over the second system, at the cost of one exponentiation.

DOI:10.1049/ip-i-2.1992.0008

出版商:IEE    

年代:1992

数据来源: IET

摘要:

An analytical method for investigating slotted ALOHA land-mobile networks is presented. The probability of successful reception and throughput is assessed for a single base station, taking account of contending transmissions and receiver noise. Receiver capture is assumed to occur if the received signal power exceeds the joint interference power by a certain margin, called the receiver threshold. Rayleigh fading and UHF groundwave propagation are considered. Results are extended for a cellular network considering the interference from packet transmissions in other (co-channel) cells. It is seen that in packetswitched cellular nets, frequency re-use distances may be substantially smaller than in circuitswitched (CW) telephony networks, where each cell has to be safeguarded continuously from cochannel interference. Moreover, a technique to assess the throughput of ALOHA networks with multiple, geographically-separated base stations is presented and numerical results are given for uniform Poisson-distributed packet transmissions in the service area.

DOI:10.1049/ip-i-2.1992.0009

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Diversity is a well known technique to mitigate the deleterious effects of the radio channel as it can reduce the signal variability. However, the improvement in performance obtainable from the use of microscopic diversity is related to the standard deviation (σ) of the lognormal component, the improvement decreasing as σ increases. In this paper a closed-form analytical solution is obtained for the performance ofMbranch macroscopic selection diversity. It has been found that a composite Rayleigh plus lognormal distribution can be accurately approximated by another log-normal distribution. The results indicate that for a BER of 10−3and (σ = 9 dB, a 2-branch macroscopic diversity offers an improvement of 13 dB. Unlike microscopic diversity, the performance improvement of anMbranch macroscopic system increases as σ increases. The results also show that, for the same number of branches, macroscopic outperforms microscopic diversity and the composite microscopic plus macroscopic systems.

DOI:10.1049/ip-i-2.1992.0010

出版商:IEE    

年代:1992

数据来源: IET