Canny Edge Detector - Development of The Canny Algorithm

Development of The Canny Algorithm

Canny's aim was to discover the optimal edge detection algorithm. In this situation, an "optimal" edge detector means:

• good detection – the algorithm should mark as many real edges in the image as possible.
• good localization – edges marked should be as close as possible to the edge in the real image.
• minimal response – a given edge in the image should only be marked once, and where possible, image noise should not create false edges.

To satisfy these requirements Canny used the calculus of variations – a technique which finds the function which optimizes a given functional. The optimal function in Canny's detector is described by the sum of four exponential terms, but can be approximated by the first derivative of a Gaussian.