In the framework of the GLAUCAD project the following software and algorithm were developed:
- Automatic papilla detection software:
This software contains a robust algorithm for detecting the papilla area within a colour fundus image automatically. Tests were performed on thousands of images with varying qualities. The results show a very good estimation of the papilla area for a very large fraction of the image database.
- 3D alignment software (Matlab prototype):
Due to non-constant exposure conditions of the stereo slides and parameter estimations within the stereo reconstruction process, the resulting topographies have different depth scaling. This fact complicates the objective to extract parameters, which are capable to indicate smallest changes over time within a sequence of topographies. As a post-calibration approach failed, the only chance was a registration (affine transformation) by using constant features. For this, the retina area outside the disc was used. The method is to use the first topography of a sequence as reference and to align the following topographies to this one. For the registration itself a grid around the papilla (disc) area is defined in the reference topography and the corresponding points in the topography to be registered are found by calculating correlation coefficients in the color images. To find the complete 3D co-ordinates the corresponding z values of the topography are used. The distance function to be minimized is the sum of squared distances between the corresponding 3D co-ordinates. The distances itself are functions of the transformation parameters (translation, rotation, scaling).
- Program for 3D sphere approximation:
A universal algorithm to approximate an implicitly defined surface to a cloud of 3D co-ordinates was developed. Given a (initial) set of parameters to be optimised, this algorithm calculates the closest distance of the points to the surface (normal direction). The squares of these distances are summed to a distance function, which is dependent on the parameters to be optimised. These parameters are separated in shape, translation and rotation parameters.