Circular Region Extraction Using a Filtered Radial Gradient Method

An algorithm for the extraction of a circular region of an image using a filtered radial gradient method is described and applied to posterior capsule opacification images of the eye. 1 Introduction Cataract formation within the lens of the eye is commonly treated by surgery: the lens is removed and replaced by an intraocular lens inserted within the lens capsule. Over a period of months the capsule contracts onto the artificial lens. The posterior lens capsule has a propensity to thicken leading to a reduction in the patient visual acuity. Remedial treatment may be via a YAS laser to make an aperture. The condition occurs within the first two years in 20--50% of patients. The condition may be detected using an opthalmic camera that has been modified to incorporate a digital CCD detector array. The camera records digital images of the posterior lens capsule of a patients eye. The objective of the present work has been to develop an automatic system of image analysis to recognise and q..

An Implementation of the Active Contour Method for Noisy Images using a Local Minimisation Algorithm

An active contour (also known as a snake) is a deformable curve which is to be located on the external boundary of an object. This delimiting curve can then be used to extract the object from an (noisy) image. This note presents an implementation of the active contour method using a local minimisation algorithm in the MATLAB system together with an application to posterior capsule opacification images. 1 Introduction One method of extracting an object or collection of objects from a noisy image is the contour extracting method known as the active contour model introduced in the seminal paper of Kass et al. [1]. More recent developments utilised in this work are presented in Lai and Chin [2,3], and Williams and Shah [4]. An active contour, also known as a snake, is a deformable line modified by internal "forces" resulting from the geometry of the curve (the distance between points, the curvature, etc.) and image forces due primarily to the intensity gradient, that is, to the edge stren..