Line Color and Shading

In almost all technical illustrations, lines are drawn in black. Occasionally, if the illustration incorporates shading, another convention may apply in which some interior lines are drawn in white, like a highlight. This technique may be the representation of the real white highlights as can be seen on edges of the mechanical part in Figure 8. By using this convention, lines drawn in black and white suggest a light source, and denote the model's orientation. For example, Figure 9 shows how an artist may use white for interior lines, producing a highlight.

  

Figure 8: This photograph of a metal object shows the anisotropic reflections and the white edge highlights which illustrators sometimes depict.

  

Figure: Left: Illustrators sometimes use the convention of white interior edge lines to produce a highlight. Courtesy of Macmillan Reference USA, a division of Ahsuog, Inc. [23]. Right: An image produced by our system, including shading, silhouettes, and white crease lines.

Another example is shown in Figure 9, comparing an illustration produced by an artist and an image from our system in which white creases are drawn.