Bump mapping is a

texture mapping Texture mapping is a term used in computer graphics to describe how 2D images are projected onto 3D models. The most common variant is the UV unwrap, which can be described as an inverse paper cutout, where the surfaces of a 3D model are cut ap ...

technique in

computer graphics Computer graphics deals with generating images and art with the aid of computers. Computer graphics is a core technology in digital photography, film, video games, digital art, cell phone and computer displays, and many specialized applications. ...

for simulating bumps and wrinkles on the surface of an object. This is achieved by perturbing the

surface normal In geometry, a normal is an object (e.g. a line, ray, or vector) that is perpendicular to a given object. For example, the normal line to a plane curve at a given point is the infinite straight line perpendicular to the tangent line to the ...

s of the object and using the perturbed normal during lighting calculations. The result is an apparently bumpy surface rather than a smooth surface, although the surface of the underlying object is not changed. Bump mapping was introduced by James Blinn in 1978.Blinn, James F
"Simulation of Wrinkled Surfaces"
Computer Graphics, Vol. 12 (3), pp. 286-292

SIGGRAPH SIGGRAPH (Special Interest Group on Computer Graphics and Interactive Techniques) is an annual conference centered around computer graphics organized by ACM, starting in 1974 in Boulder, CO. The main conference has always been held in North ...

-ACM (August 1978)

Normal mapping In 3D computer graphics, normal mapping, or Dot3 bump mapping, is a texture mapping technique used for faking the lighting of bumps and dents – an implementation of bump mapping. It is used to add details without using more polygonal modeling, ...

is the most common variation of bump mapping used.

Principles

Bump mapping is a technique in

to make a rendered surface look more realistic by simulating small displacements of the surface. However, unlike displacement mapping, the surface geometry is not modified. Instead only the surface normal is modified as if the surface had been displaced. The modified surface normal is then used for lighting calculations (using, for example, the

Phong reflection model The Phong reflection model (also called Phong illumination or Phong lighting) is an empirical model of the local illumination of points on a surface designed by the computer graphics researcher Bui Tuong Phong. In 3D computer graphics, it is ...

) giving the appearance of detail instead of a smooth surface. Bump mapping is much faster and consumes fewer resources for the same level of detail compared to displacement mapping because the geometry remains unchanged. There are also extensions which modify other surface features in addition to increasing the sense of depth. Parallax mapping and horizon mapping are two such extensions. The primary limitation with bump mapping is that it perturbs only the surface normals without changing the underlying surface itself.Real-Time Bump Map Synthesis
Jan Kautz¹, Wolfgang Heidrichy² and Hans-Peter Seidel¹, (¹Max-Planck-Institut für Informatik, ²University of British Columbia) Silhouettes and shadows therefore remain unaffected, which is especially noticeable for larger simulated displacements. This limitation can be overcome by techniques including displacement mapping where bumps are applied to the surface or using an isosurface.

Methods

There are two primary methods to perform bump mapping. The first uses a height map for simulating the surface displacement yielding the modified normal. This is the method invented by Blinn and is usually what is referred to as bump mapping unless specified. The steps of this method are summarized as follows. Before a lighting calculation is performed for each visible point (or

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...

) on the object's surface: # Look up the height in the

heightmap In computer graphics, a heightmap or heightfield is a raster image used mainly as Discrete Global Grid in secondary elevation modeling. Each pixel stores values, such as surface elevation data, for display in 3D computer graphics. A height ...

that corresponds to the position on the surface. # Calculate the surface normal of the heightmap, typically using the

finite difference A finite difference is a mathematical expression of the form . Finite differences (or the associated difference quotients) are often used as approximations of derivatives, such as in numerical differentiation. The difference operator, commonly d ...

method. # Combine the surface normal from step two with the true ("geometric") surface normal so that the combined normal points in a new direction. # Calculate the interaction of the new "bumpy" surface with lights in the scene using, for example, the

. 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.

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 In computer science, a lookup table (LUT) is an array data structure, array that replaces runtime (program lifecycle phase), runtime computation of a mathematical function (mathematics), function with a simpler array indexing operation, in a proc ...

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

External links

Bump shading for volume textures
Max, N.L., Becker, B.G., Computer Graphics and Applications, IEEE, Jul 1994, Volume 14, Issue 4, pages 18 – 20, ISSN 0272-1716

* ttp://www.neilwallis.com/projects/java/bump/index.php Bump Mapping example(

Java applet Java applets were applet, small applications written in the Java (programming language), Java programming language, or another programming language that Compiled language, compiles to Java bytecode, and delivered to users in the form of Ja ...

) {{DEFAULTSORT:Bump Mapping Demo effects Texture mapping Virtual reality

Principles

Methods

Realtime bump mapping techniques

See also

References

External links