Two-tier tissue decomposition for histopathological image representation and classification

In digital pathology, devising effective image representations is crucial to design robust automated diagnosis systems. To this end, many studies have proposed to develop object-based representations, instead of directly using image pixels, since a histopathological image may contain a considerable amount of noise typically at the pixel-level. These previous studies mostly define their objects, based on the color information, as to approximately represent histological tissue components in an image and then use the spatial distribution of these objects for image representation and classification. Thus, object definition has a direct effect on the way of representing the image, which in turn affects classification accuracies. In this thesis, we present a new model for effective representation and classification of histopathological images. The contributions of this model are twofold. First, it introduces a new two-tier tissue decomposition method for defining a set of multityped objects in an image. Different than the previous studies, these objects are defined combining the texture, shape, and size information and they may correspond to individual histological components as well as tissue sub-regions of different characteristics. As its second contribution, it defines a new metric, which we call “dominant blob scale”, to characterize the shape and size of an object with a single scalar value. Our experiments on colon tissue images reveal that this new object definition and characterization provides distinguishing representation of normal and cancerous histopathological images, which is effective to obtain more accurate classification results compared to its counterparts.