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Quantification of vessel density helps to know the stage of the disease during diagnosis and patient's response to treatment. However, this requires presence of all vessels in the image. The available segmentation techniques that are manual based are prone to errors, tiresome and slow, while some that are automated do face difficulty in distinguishing the vessel tissue from the non-vessel tissue due to the presence of intensity inhomogeneity and noise in images. Therefore, there is need for improved segmentation methods that can extract all sizes of vessels for better quantification of the vessel density and improved decision making during diagnosis. In this paper, a 3D hybrid approach for segmentation has been developed, based on white top hat scale space hessian vessel enhancement filter and multithreshold Otsu method. The hybrid method can address the intensity inhomogeneity, as a result, more vessels of different sizes are detected. The method is also robust and able to detect abnormalities in the vessels.

Due to the increasing demand for competent vessel segmentation techniques, it is important to review some of the available segmentation techniques. This paper presents a survey of the state-of-art vessel segmentation techniques. In this paper, vessel segmentation techniques are categorized into three classes. These are; Model based segmentation approaches, Tracking based segmentation approaches and Pattern recognition approaches. The three categories identified are never independent. Some of the methods are combined with others to aid segmentation. A contextual analysis is done exploring techniques in-terms of strengths and weaknesses. The summary highlights research gaps that need attention.

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Stain in-homogeneity adversely affects segmentation and quantification of tissues in histology images. Stain normalisation techniques have been used to standardise the appearance of images. However, most the available stain normalisation techniques only work on a particular kind of stain images. In addition, some of these techniques fail to utilise both the spatial and textural information in histology images, leading to image tissue distortion. In this paper, a hybrid approach has been developed, based on an octree colour quantisation algorithm combined with the Beer-Lambert law, a modified blind source separation algorithm, and a modified colour transfer approach. The hybrid method consists of two stages the stain separation stage and colour transfer stage. An octree colour quantisation algorithm combined with Beer-Lambert law, and a modified blind source separation algorithm are used during the stain separation stage to computationally estimate the amount of stain in an histology image based on its chromatic and luminous response. A modified colour transfer algorithm is used during the colour transfer stage to minimise the effect of varying staining and illumination. The hybrid method addresses the colour variation problem in both H&DAB (Haemotoxylin and Diaminobenzidine) and H&E (Haemotoxylin and Eosin) stain images. The stain normalisation method is validated against ground truth data. It is widely known that the Beer-Lambert law applies to only stains (such as haematoxylin, eosin) that absorb light. We demonstrate that the Beer-Lambert law applies is applicable to images containing a DAB stain. Better stain normalisation results are obtained in both H&E and H&DAB images.