Abstract: We propose a simple and interactive technique for volume illustration by using the difference between the original intensity values and a low-pass filtered copy. This difference, known as unsharped mask, provides us with a spatial importance map that captures salient and separability information about regions in the volume. We integrate this map in the visualization pipeline and use it to modulate the color and the opacity assigned by the transfer function to produce different illustrative effects. We also apply stipple rendering modulating the density of the dots with the spatial importance map. The core of our approach is the computation of a 3D Gaussian filter, which is equivalent to three consecutive 1D filters. This separability feature allows us to obtain interactive rates with a CUDA implementation. We show results of our approach for different data sets.