3D graphics eBook - Course Materials Repository

Bump mapping 27
4. Calculate the interaction of the new "bumpy" surface with lights in the scene using, for example, the Phong
reflection model.
The result is a surface that appears to have real depth. The algorithm also ensures that the surface appearance
changes as lights in the scene are moved around.
The other method is to specify a normal map which contains the modified normal for each point on the surface
directly. Since the normal is specified directly instead of derived from a height map this method usually leads to
more predictable results. This makes it easier for artists to work with, making it the most common method of bump
mapping today [2] .
There are also extensions which modifies other surface features in addition to increase the sense of depth. Parallax
mapping is one such extension.
The primary limitation with bump mapping is that it perturbs only the surface normals without changing the
underlying surface itself. [3] Silhouettes and shadows therefore remain unaffected, which is especially noticeable for
larger simulated displacements. This limitation can be overcome by techniques including the displacement mapping
where bumps are actually applied to the surface or using an isosurface.
Realtime bump mapping techniques
Realtime 3D graphics programmers often use variations of the technique in order to simulate bump mapping at a
lower computational cost.
One typical way was to use a fixed geometry, which allows one to use the heightmap surface normal almost directly.
Combined with a precomputed lookup table for the lighting calculations the method could be implemented with a
very simple and fast loop, allowing for a full-screen effect. This method was a common visual effect when bump
mapping was first introduced.
References
[1] Blinn, James F. "Simulation of Wrinkled Surfaces" (http:/ / portal. acm. org/ citation. cfm?id=507101), Computer Graphics, Vol. 12 (3),
pp. 286-292 SIGGRAPH-ACM (August 1978)
[2] Mikkelsen, Morten. Simulation of Wrinkled Surfaces Revisited (http:/ / image. diku. dk/ projects/ media/ morten. mikkelsen. 08. pdf), 2008
(PDF)
[3] Real-Time Bump Map Synthesis (http:/ / web4. cs. ucl. ac. uk/ staff/ j. kautz/ publications/ rtbumpmapHWWS01. pdf), Jan Kautz 1 , Wolfgang
Heidrichy 2 and Hans-Peter Seidel 1 , ( 1 Max-Planck-Institut für Informatik, 2 University of British Columbia)
External links
• Bump shading for volume textures (http:/ / ieeexplore. ieee. org/ xpl/ freeabs_all. jsp?arnumber=291525), Max,
N.L., Becker, B.G., Computer Graphics and Applications, IEEE, Jul 1994, Volume 14, Issue 4, pages 18 - 20,
ISSN 0272-1716
• Bump Mapping tutorial using CG and C++ (http:/ / www. blacksmith-studios. dk/ projects/ downloads/
bumpmapping_using_cg. php)
• Simple creating vectors per pixel of a grayscale for a bump map to work and more (http:/ / freespace. virgin. net/
hugo. elias/ graphics/ x_polybm. htm)
• Bump Mapping example (http:/ / www. neilwallis. com/ java/ bump2. htm) (Java applet)