Optic disk segmentation is a prerequisite step in automatic retinal screening systems. In this paper, we propose an algorithm for optic disk segmentation based on a local adaptive thresholding method. Location of the optic disk is validated by intensity and average vessel width of retinal images. Then an adaptive thresholding is applied on the temporal and nasal part of the optic disc separately. Adaptive thresholding, makes our algorithm robust to illumination variations and various image acquisition conditions. Moreover, experimental results on the DRIVE and KHATAM databases show promising results compared to the recent literature. In the DRIVE database, the optic disk in all images is correctly located and the mean overlap reached to 43.21 . The optic disk is correctly detected in 98 of the images with the mean overlap of 36.32 in the KHATAM database.
Active contour methods work on a gradient of the image and lock onto homogenous region enclosed by strong gradient information. Since the gradient along the optic disk boundary is not homogeneous, active contour methods should be modified or combined with other methods. @cite_6 and @cite_1 used morphological operation to address this problem. However, using morphological operations can also blur and change the location of the optic disk boundary. Therefore, the result of optic disk boundary segmentation is not reliable.
@cite_1 @cite_6
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An efficient optic disk localization and segmentation are important tasks in an automated retinal image analysis system. General-purpose edge detection algorithms often fail to segment the optic disk due to fuzzy boundaries, inconsistent image contrast or missing edge features. This paper presents a method to automatically locate and boundary detect of the optic disk. The detection procedure comprises two independent methodologies. On one hand, a location methodology obtains a pixel that belongs to the OD using iterative thresholding method followed by Principal Component Analysis techniques (PCA) and, on the other hand, a boundary segmentation methodology estimates the OD boundary by applying region-based active contour model in a variational level set formulation (RSF). The method uses an improved geometric active contour model which can not only solve the boundary leakage problem but also is less sensitive to intensity inhomogeneity The results from the RSF method were compared with conventional optic disk detection using a geometric active contour models (ACM) and later verified with hand-drawn ground truth. Results indicate 89 accuracy for identification and 95.05 average accuracy in localizing the optic disc boundary. The location of the optic disc is of critical importance in retinal image analysis. In this work we improve on an approach introduced by Mendels, Heneghan and Thiran (1999) which localises an optic disc region through grey level morphology, followed by snake fitting. We propose and implement both the automatic initialisation of the snake and the application of morphology in colour space. We examine various methods of performing the morphology step (to remove the interference of blood vessels) and compare them against each other. We demonstrate that our proposed simple Lab colour morphology method is particularly suitable for the characteristics of our optic disc images. Results indicate 90.32 average accuracy in localising, the optic disc boundary.