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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  which requires the mere
convolution of a small kernel (3
3 pixels) over the image.
Alternatively, more computationally intensive contour detection techniques are
available such as the Deriche  or Canny  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.