Subpixel Catadioptric Modeling Of High Resolution Corneal Reflections

We present a calibration procedure that achieves a sub-pixel accurate model of the catadioptric imaging system defined by two corneal spheres and a camera. First, the eyes' limbus circles are used to estimate the positions of the corneal spheres. Then, corresponding features in the corneal reflections are detected and used to optimize the corneal spheres' positions with a RANSAC framework customized to the corneal catadioptric model. The framework relies on a bundle adjustment optimization that minimizes the corneal reflection reprojection error of corresponding features. In our experiments, for images with a total resolution of 5,472 x 3, 648, and a limbus resolution of 600 x 600, our calibration procedure achieves an average reprojection error smaller than one pixel, over hundreds of correspondences. We demonstrate the calibration of the catadioptric system in the context of sparse, feature-based, and dense, pixel-based reconstruction of several 3D scenes from corneal reflections.