To detect the iris with the Circular Hough Transformation it is necessary to transform the region from a colored to a gray scale image. Most image processing algorithms are applied on gray scale or binary images because they contain less information than colored images. Hereafter, possible image artifacts are removed with a Gaussian filter. Now, the iris can be highlighted by an edge-detector, here the Canny filter. The result of the Canny filter has the benefit that edges are represented as one pixel wide lines (also called binary edges). The image delivered by this pre-processing step forms the basis for the subsequent circle detection.