Feature Based Segmentation of Colour Textured Images using Markov Random Field Model

Abstract

The problem of image segmentation has been investigated with a focus on colored textured image segmentation.Texture is a substantial feature for the analysis of different types of images. Texture segmentation has an assortment of important applications ranging from vision guided autonomous robotics and remote sensing to medical diagnosis and retrieval in large image databases. But the main problem with the textured images is that they contain texture elements of various sizes and in some cases each of which can itself be textured.Thus the texture image segmentation is widely discerned as a difficult and thought-provoking problem.In this thesis an attempt has been made to devise methodologies for automated color textured image segmentation scheme. This problem has been addressed in the literature, still many key open issues remain to be investigated. As an initial step in this direction, this thesis proposes two methods which address the problem of color texture image segmentation through feature extraction approach in partially supervised approach.The feature extraction approaches can be classified into feature based and model based techniques.In feature based technique features are assessed without any model in mind. But in case of model based approach an inherent mathematical model lets eatures to be measured by fitting the model to the texture.The inherent features of the texture are captured in a set of parameters in order to understand the properties generating the texture. Nevertheless, a clear distinction can not be made between the two approaches and hence a combination of approaches from different categories is frequently adopted. In textured image segmentation, image model assumes a significant role and is developed by capturing salient spatial properties of an image. Markov random field (MRF)theory provides a convenient and consistent way to model context dependent entities.In this context a new scheme is proposed using Gaussian MRF model where the segmentation problem is formulated as a pixel labeling problem.The a priori class labels are modeled as Markov random field model and the number of classes is known a priori in partially supervised framework.The image label estimation problem is cast in Bayesian framework using Maximum a Posteriori (MAP)criterion and the MAP estimates of the image labels are obtained using iterated conditional modes (ICM) algorithm. Though the MRF model takes into account the local spatial interactions, it has a limitation in modeling natural scenes of distinct regions. Hence in our formulation, the first scheme takes into account within and between color plane interactions to incorporate spectraland contextual features. Genetic algorithm is employed for the initialization of ICM algorithm to obtain MAP estimates of image labels. The faster convergence property of the ICM algorithm and global convergence property of genetic algorithm are hybridized to obtain segmentation with better accuracy as well as faster convergence.