Edge Detection

The extraction of edges or contours from a two dimensional array of pixels (a gray-scale image) is a critical step in many image processing techniques. A variety of computations are available which determine the magnitude of contrast changes and their orientation. Extensive literature exists documenting the available operators and the post-processing methods to modify their output. A trade-off exists, though, between efficiency and quality of the edge detection. Fast and simple edge detection can be performed by filters such as the popular Sobel operator [25] which requires the mere convolution of a small kernel (3 $\times$ 3 pixels) over the image. Alternatively, more computationally intensive contour detection techniques are available such as the Deriche [11] or Canny [6] method. These detectors require that a set of parameters be varied to detect the desired scale and curvature of edges in the image. It is necessary to compare the simple Sobel detector and the complex Deriche-type detectors before selecting the edge detection scheme of preference.