Nonlinear registration for scanned retinal images: application to ocular polarimetry

Retinal images of approximately 1 degrees of visual field were recorded with a homemade scanning laser ophthalmoscope. The benefit of using a nonlinear registration technique to improve the summation process when averaging frames, rather than a standard approach based on correlation, was assessed. Results suggest that nonlinear methods can surpass linear transformations, allowing improved contrast and more uniform image quality. The importance of this is also demonstrated with specific polarization measurements to determine the degree of polarization across an imaged retinal area. In such a context, where this parameter of polarization is extracted from a combination of registered images, the benefit of the nonlinear method is further increased.