Practical Algorithms for 3D Computer Graphics, 2nd Edition

122 4. Basic visualization

Figure 4.21: After lighting and P h o n g shading have been added to a hidden surface

rendering, the imag e starts to look much more realistic.

you look at the outlines of both spheres you will see that they are made from

straight segments. In th e case of the smooth looking sphere it is because the

discontinuities in shading between adjacent facets have been eliminated that it

looks smooth. To the eye a discontinuity in shading is much more noticeable

than a small angular change between two edges.

So how is the smooth shading achieved? There are two useful possibili-

ties: one, th e Phong approach, gives a more realistic