The zero-crossing test of the second directional derivative is regarded by many image processing researchers as the optimal method of edge detection. Fast implementation of a zero-crossing detector for an image that has been operated upon by a Laplacian of Gaussian (LOG) convolution is difficult; execution speed is, in fact, the primary disadvantage of edge detection by LOG. Another drawback to this method is the difficulty in programming the algorithm itself. Use of efficient library functions to perform the required LOG convolutions and tradeoffs between multiple cascaded filters and a single filter with a spatially large impulse response will be examined. Finally, a convolution and look-up table-based implementation of a zero-crossing detector will be explained.