In his blog post and in the discussion that follows, Matt brings up an interesting question about finding the best way for parameter selection.
For the lack of a better approach, parameter selection in seismic attributes is just an interactive game. In the Madagascar version, the key parameter for the Canny edge detector is the amount of prior anisotropic-diffusion smoothing, controlled by the smoothing radius (rect= parameter.) We can do different things with it: for example, make a movie of different images looping through different values of the radius, or, by exposing the parameter to the command-line SCons interface, build a simple GUI script for controlling it. The question posted by Matt waits for a better answer.