An Efficient Approach to Detect Optic Disc in Digital Colour Images of the Human Retina

Detection of Optic Disc (OD) is an essential step in the automatic analysis of digital colour fundus mages, while developing automated screening systems for diabetic retinopathy. The main objective of this research is to automatically detect the position of the OD. The method starts by normalizing luminosity and contrast throughout the image using illumination equalization and adaptive histogram equalization methods respectively. The OD detection algorithm is based on matching the expected directional pattern of the retinal blood vessels. Hence, a simple matched filter is proposed to roughly match the direction of the vessels at the OD vicinity. The retinal vessels are segmented using a simple and standard 2-D Gaussian matched filter. Consequently, a vessels direction map of the segmented retinal vessels is obtained using the same segmentation algorithm. The segmented vessels are then thinned and filtered using local intensity, to represent finally the OD center candidates. The difference between the proposed matched filter resized into four different sizes and the vessels directions at the surrounding area of each of the OD- center candidates is measured. The minimum difference provides an estimate of the OD center coordinates. The proposed method was implemented in MATLAB.