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This document presents a comprehensive study on retinal image registration and vessel enhancement techniques, focusing on algorithms such as "Multiscale vessel enhancement filtering" and "Feature-Based Retinal Image Registration Using Bifurcation Structures." It details the methodologies for extracting key features from vascular structures, applying affine transformations for accurate registration, and utilizing local image descriptors. Central to the analysis is the exploration of bifurcation structures in retinal images, leading to effective matching and greater precision in vascular tree extraction.
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July 15, 2011 Registering retinal images Babak Ghafaryasl Universitat Pompeu Fabra Csaba Molnár University of Szeged Antonio R. Porras Universitat Pompeu Fabra Arie Shaus Tel Aviv University http://www.inf.u-szeged.hu/projectdirs/ssip2011/teamG
Vessel enhancement “Multiscale vessel enhancement filtering”, Frangi et al, 1998 • - Scale Space representation • Local image descriptors • - Eigenvalues of Hessain (2nd derivative) matrix • Tubular, plate-like and spherical structures
Vascular tree extraction Original images Vessel enhancement Thresholding + Skeletonization + Largest connected components
From bifurcation point to bifurcation structure… “Feature-Based Retinal Image Registration Using Bifurcation Structures”, Chen & Zhang, 2009 L2 L3 • But… • L’s are normalized to sum up to 1. • The α triplets sum up to 360. • Therefore we can remove some redundancy. L1 We can measure a distance between such structures!
From bifurcation structures to registration… Step 1: Find bifurcation structures in both images. Step 2: Find the best match between two bifurcation structures. The match between 4 points (3 are enough) determines the affine transformation. Step 3: Find next best matches (taking the transformation into account); refine the affine transformation with more points.
Results: feature extration All candidates Vessel registration Matching candidates