Automatic generation of pencil drawing using LIC

Line Integral Convolution (LIC)[Cabral and Leedom 1993]] is a texture based vector field visualization technique. Why using LIC for pencil drawing generation? Let us look at the two images shown in Figure 1. Figure 1(a) is a digitized sample of a real pencil drawing. Look over it, we can perceive the traces of parallel pencil strokes and a gray scale tone built with the strokes. If we look at any local area of the image, however, we can find that the direction of strokes and the intensity of pixels vary randomly. The variance of intensity results from the interaction of lead material and drawing paper. The LIC image shown in Figure 1(b), however, presents the very similar features. Since an LIC image is obtained by low-pass filtering a white noise along the streamlines of a vector field, we can see traces along streamlines. On the other hand, the intensities of pixels within any local area vary randomly as the input image is a white noise. Such similarity suggests us that we can imitate the tone of pencil drawings with an LIC image.