An important aspect of the lighting model is reducing the dynamic range of the luminance to make edges and highlights more distinct. Edges can be further emphasized by outlining the silhouette and boundary edges in a dark color. Some algorithms for drawing silhouette lines are described in Section 7.4. Additional algorithms using image processing techniques are described in  and can be implemented using the OpenGL pipeline as described in Section 13. [40,65] discuss software methods for extracting silhouette edges which can then be drawn as lines.