To ensure that the result images, such as Figure 7 and 16, are comparable, I process identical image volumes for all computations. All results are represented by the same image sections of the image volume.
Usually, each processing step offers its user a set of configurable parameters. In the case of the gradient magnitude operator, users can set individual weights for each partial derivative term or choose among competing finite-difference approximations of the partial derivatives. In general, I experiment with such processing parameters. Because of the shear amount of possible combinations, such experiments are usually not exhaustive. The result images that I include in this report are the best results that I found. Similarly, I choose individual display parameters, such as polarity and clip, for each image.