Video of the labelling of projected Placido rings through the scanning annulus

The Elliptical Scanning Algorithm is an effective method to individually detect and label the projected rings. It consecutively defines an elliptical annulus of one pixel wide which grows pixel by pixel and sweeps the image, from centre to periphery, until it detects and labels each whole ring. In a way, it works like a snake-annealing algorithm. Active contour models (snakes) are energy-minimising curves that deform to fit image features. Elliptical Scanning Algorithm changes its geometry in order to label reflected rings.

The authors would like to acknowledge the financial support of the Spanish Ministerio de Ciencia e Innovación through the project FIS2009-05639-ET and BIA2011-22704,, the Generalitat Valenciana through the project PROMETEO/2011/021 and the University of Alicante through the project GRE10-09. A.B. Roig thanks Fundación Cajamurcia the grant “Beca de investigación Cajamurcia 2010”.