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Digital image feature detectors often comprise two stages of processing: an initial filtering phase and a secondary search stage. The initial filtering is designed to accentuate specific feature characteristics or suppress spurious components of the image signal. The second stage of processing involves searching the results for various criteria that will identify the locations of the image features. The local energy feature detection scheme combines the squares of the signal convolved with a pair of filters that are in quadrature with each other. The resulting local energy value is proportional to phase congruency which is a measure of the local alignment of the phases of the signals constituent Fourier components. Points of local maximum phase alignment have been shown to correspond to visual features in the image. The local energy calculation accentuates the location of many types of image features, such as lines, edges and ramps and estimates of local energy can be calculated in multidimensional image data by rotating the quadrature filters to several orientations. The second stage search criterion for local energy is to locate the points that lie along the ridges in the energy map that connect the points of local maxima. In three dimensional data the relatively higher energy values will form films between connecting laments and tendrils. This thesis examines the use of recursive spatial domain filtering to calculate local energy. A quadrature pair of filters which are based on the first derivative of the Gaussian function and its Hilbert transform, are rotated in space using a kernel of basis functions to obtain various orientations of the filters. The kernel is designed to be separable and each term is implemented using a recursive digital filter. Once local energy has been calculated the ridges and surfaces of high energy values are determined using a flooding technique. Starting from the points of local minima we perform an ablative skeletonisation of the higher energy values. The topology of the original set is maintained by examining and preserving the topology of the neighbourhood of each point when considering it for removal. This combination of homotopic skeletonisation and sequential processing of each level of energy values, results in a well located, thinned and connected tracing of the ridges. The thesis contains examples of the local energy calculation using steerable recursive filters and the ridge tracing algorithm applied to two and three dimensional images. Details of the algorithms are contained in the text and details of their computer implementation are provided in the appendices.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 55-58). Also available in electronic version. Access restricted to campus users.

Thesis (M.S.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 62-64)

Thesis (DTech(Business Informatics))--Cape Technikon, Cape Town, 1997 / Modem applications in computer graphics and telecommunications command high performance filtering and smoothing to be implemented. The recent development of a new class of max-min selectors for digital image processing is investigated with special emphasis on the practical implications for hardware and software design.

Many applications of image processing require the initial segmentation of the image by means of grey-level thresholding. In this thesis, the problems of automatic threshold selection and evaluation are addressed in order to find a universally applicable thresholding method. Three previously proposed threshold selection techniques are investigated, and two new methods are introduced. The results of applying these methods to several different images are evaluated using two threshold evaluation techniques, one subjective and one quantitative. It is found that no threshold selection technique is universally acceptable, as different methods work best with different images and applications

M.Ing. / This dissertation proposes a marker-free visual based interface device to be used with menu driven systems. This system, called HandsFree, uses the Graphics Processing Unit (GPU) together with Shader technology to perform the image processing. HandsFree makes use of a web camera to gain user input without requiring elementary computer skills. Background subtraction was used to extract user input from the images. The problems usually obtained with background subtraction were overcome by using an averaging technique. Test results proved HandsFree to be robust against different coloured backgrounds and skin tones, different lighting intensity and sudden change in lighting intensity.

Currently, standard enhancement of three-channel colour digital imagery is not performed in a general fashion; it is dependent on the particular colour device used to display the imagery. By introducing a colour transformation, the enhancement can be standardized and therefore be defined in terms of other devices. In addition, the colour transformation can be defined such that the perceptual attributes of colour associated with an image are more easily manipulated. The purpose of this work is to examine a variety of such colour transformations and implement a subset of these on a colour CRT. / Science, Faculty of / Computer Science, Department of / Graduate

M. Ing. (Mechanical Engineering) / This research aims at identifying techniques which can be used to remove rain from a digitized rain distorted image. The research commenced with computer implemented rain removal techniques but also lead to camera obscuration techniques. Camera rain obscuration technique: Before a rainy scene is digitized, rain can be removed from the projected image by the correct selection of camera aperture and shutter speed settings. These settings will determine the way the real image is transformed through the lens and onto the recording plane. Computer image restoration technique: Rain removal after digitization is performed in both the frequency and the spatial domain by means of two dimensional image processing and filtering techniques. Time consuming frequency domain techniques were replaced by equivalent convolutional techniques. Experiments on simulated and real scenes corrupted with rain indicated that it is possible to improve the image appearance with only a marginal decrease in signal to noise ratio.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy