focus many of these are u201c edge detection u201d algorithms examples of edge detection algorithms can be found in fundamentals of digital image processing by anil k jain the entirety of which is incorporated here by reference one algorithm uses gradient operators to detect edges gradient operators are masks or simple matrices used to generate a gradient map gradient operators when convolved with pixels in an image yield a gradient map in two orthogonal directions similarly compass operators yield a gradient map in a selected number of directions that correspond to compass directions once the gradient has been calculated an edge is identified by searching for those spots where the gradient exceeds some threshold the level of focus generally corresponds to the severity of the gradient other edge detection algorithms apply a second order derivative to the image the derivative detects rates of change in pixel intensity across the image again the algorithm usually convolves the image with an operator edges are identified by locations where the gradient exceeds some threshold or more commonly by searching for spots where the second derivative wave form crosses zero while zero crossings are useful to detect edges they only return a binary value and therefore do not convey precise.