Bump mapping is a

texture mapping Texture mapping is a method for mapping a texture on a computer-generated graphic. Texture here can be high frequency detail, surface texture, or color. History The original technique was pioneered by Edwin Catmull in 1974. Texture mappi ...

technique in

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

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 such as 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) line perpendicular to the tangent line to the curve ...

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 James F. Blinn (born 1949) is an American computer scientist who first became widely known for his work as a computer graphics expert at NASA's Jet Propulsion Laboratory (JPL), particularly his work on the pre-encounter animations for the Voya ...

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 on computer graphics (CG) organized by the ACM SIGGRAPH, starting in 1974. The main conference is held in North America; SIGGRAPH Asia ...

-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 polygons. A common ...

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 so ...

) giving the appearance of detail instead of a smooth surface. Bump mapping is much faster and consumes less 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 Parallax mapping (also called offset mapping or virtual displacement mapping) is an enhancement of the bump mapping or normal mapping techniques applied to textures in 3D rendering applications such as video games. To the end user, this means t ...

and

horizon mapping The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...

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 An isosurface is a three-dimensional analog of an isoline. It is a surface that represents points of a constant value (e.g. pressure, temperature, velocity, density) within a volume of space; in other words, it is a level set of a continuous ...

Methods

There are two primary methods to perform bump mapping. The first uses a

height map 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 heightm ...

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 image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the s ...

) 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 . If a finite difference is divided by , one gets a difference quotient. The approximation of derivatives by finite differences plays a central role in finite difference methods for t ...

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 that replaces runtime computation with a simpler array indexing operation. The process is termed as "direct addressing" and LUTs differ from hash tables in a way that, to retrieve a value v w ...

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 Visual effects (sometimes abbreviated VFX) is the process by which imagery is created or manipulated outside the context of a live-action shot in filmmaking and video production. The integration of live-action footage and other live-action foota ...

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 small applications written in the Java programming language, or another programming language that compiles to Java bytecode, and delivered to users in the form of Java bytecode. The user launched the Java applet from a ...

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

Principles

Methods

Realtime bump mapping techniques

See also

References

External links