BW = edge3(V,"approxcanny",thresh) returns the edges found in the grayscale or binary volume V using the approximate Canny method. The approximate Canny method finds edges by looking for local maxima of the gradient of V. edge3 calculates the gradient using the derivative of a Gaussian smoothed volume.

The approximate Canny method uses two thresholds to detect strong and weak edges, and includes the weak edges in the output only if they are connected to strong edges. This method is more likely than the Sobel method to detect true weak edges.

BW = edge3(V,"approxcanny",thresh,sigma) returns the edges found in the intensity or binary volume V, where sigma specifies the standard deviation of the Gaussian smoothing filter. edge3 chooses the size of the filter automatically, based on sigma.

BW = edge3(V,"Sobel",thresh) accepts an intensity or a binary volume V and returns a binary volume BW with 1s where the function finds edges in V and 0s elsewhere.

The Sobel method finds edges using the Sobel approximation to the derivative. It returns edges at those points where the gradient of V is maximum. edge3 ignores all edges that are not stronger than thresh.

BW = edge3(V,"Sobel",thresh,"nothinning") speeds up the operation of the algorithm by skipping the additional edge-thinning stage. By default, or when "thinning" is specified, edge3 applies edge thinning.