Bump mapping

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A sphere without bump mapping (left). A bump map to be applied to the sphere (middle). The sphere with the bump map applied (right) appears to have a mottled surface resembling an orange. Bump maps achieve this effect by changing how an illuminated surface reacts to light, without modifying the size or shape of the surface. Bump-map-demo-full.png
A sphere without bump mapping (left). A bump map to be applied to the sphere (middle). The sphere with the bump map applied (right) appears to have a mottled surface resembling an orange. Bump maps achieve this effect by changing how an illuminated surface reacts to light, without modifying the size or shape of the surface.

Bump mapping [1] is a texture mapping technique in computer graphics for simulating bumps and wrinkles on the surface of an object. This is achieved by perturbing the surface normals 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. [2]

Contents

Normal mapping is the most common variation of bump mapping used. [3]

Principles

Bump mapping is limited in that it does not modify the shape of the underlying object. On the left, a mathematical function defining a bump map simulates a crumbling surface on a sphere, but the object's outline and shadow remain those of a perfect sphere. On the right, the same function is used to modify the surface of a sphere by generating an isosurface. This models a sphere with a bumpy surface with the result that both its outline and its shadow are rendered realistically. Bump map vs isosurface2.png
Bump mapping is limited in that it does not modify the shape of the underlying object. On the left, a mathematical function defining a bump map simulates a crumbling surface on a sphere, but the object's outline and shadow remain those of a perfect sphere. On the right, the same function is used to modify the surface of a sphere by generating an isosurface. This models a sphere with a bumpy surface with the result that both its outline and its shadow are rendered realistically.

Bump mapping is a technique in computer graphics 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) 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 and horizon mapping are two such extensions. [4]

The primary limitation with bump mapping is that it perturbs only the surface normals without changing the underlying surface itself. [5] 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 [2] 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) on the object's surface:

  1. Look up the height in the heightmap that corresponds to the position on the surface.
  2. Calculate the surface normal of the heightmap, typically using the finite difference method.
  3. Combine the surface normal from step two with the true ("geometric") surface normal so that the combined normal points in a new direction.
  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. [3]

Realtime bump mapping techniques

Example of a realtime fake bump mapping. From left: surface bitmap, intentionally blurry, source of light bitmap, bump mapping effect with light source orbiting 1 = x 2 + y 2 / x 2 {\displaystyle 1=x^{2}+y^{2}/x^{2}} trajectory. FakeBump2D-animation.gif
Example of a realtime fake bump mapping.
From left:
  1. surface bitmap, intentionally blurry,
  2. source of light bitmap,
  3. bump mapping effect with light source orbiting trajectory.

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.

See also

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Rendering or image synthesis is the process of generating a photorealistic or non-photorealistic image from a 2D or 3D model by means of a computer program. The resulting image is referred to as the render. Multiple models can be defined in a scene file containing objects in a strictly defined language or data structure. The scene file contains geometry, viewpoint, texture, lighting, and shading information describing the virtual scene. The data contained in the scene file is then passed to a rendering program to be processed and output to a digital image or raster graphics image file. The term "rendering" is analogous to the concept of an artist's impression of a scene. The term "rendering" is also used to describe the process of calculating effects in a video editing program to produce the final video output.

Gouraud shading Interpolation method in computer graphics

Gouraud shading, named after Henri Gouraud, is an interpolation method used in computer graphics to produce continuous shading of surfaces represented by polygon meshes. In practice, Gouraud shading is most often used to achieve continuous lighting on triangle meshes by computing the lighting at the corners of each triangle and linearly interpolating the resulting colours for each pixel covered by the triangle. Gouraud first published the technique in 1971.

Texture mapping Method of defining surface detail on a computer-generated graphic or 3D model

Texture mapping is a method for defining high frequency detail, surface texture, or color information on a computer-generated graphic or 3D model. The original technique was pioneered by Edwin Catmull in 1974.

The Phong reflection model 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 sometimes referred to as "Phong shading", particularly if the model is used with the interpolation method of the same name and in the context of pixel shaders or other places where a lighting calculation can be referred to as “shading”.

Phong shading Interpolation technique for surface shading

In 3D computer graphics, Phong shading is an interpolation technique for surface shading invented by the computer graphics pioneer Bui Tuong Phong. It is also called Phong interpolation, or normal-vector interpolation shading. It interpolates surface normals across rasterized polygons and computes pixel colors based on the interpolated normals and a reflection model. Phong shading may also refer to the specific combination of Phong interpolation and the Phong reflection model.

Shading Depicting depth through varying levels of darkness

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Normal mapping Texture mapping technique

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 use of this technique is to greatly enhance the appearance and details of a low polygon model by generating a normal map from a high polygon model or height map.

2.5D perspective refers to one of two things:

Reflection mapping

In computer graphics, environment mapping, or reflection mapping, is an efficient image-based lighting technique for approximating the appearance of a reflective surface by means of a precomputed texture. The texture is used to store the image of the distant environment surrounding the rendered object.

James F. Blinn 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 Voyager project, his work on the 1980 Carl Sagan documentary series Cosmos, and the research of the Blinn–Phong shading model.

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Heightmap Type of raster image in computer graphics

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 heightmap can be used in bump mapping to calculate where this 3D data would create shadow in a material, in displacement mapping to displace the actual geometric position of points over the textured surface, or for terrain where the heightmap is converted into a 3D mesh.

3D rendering Process of converting 3D scenes into 2D images

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3D computer graphics Graphics that use a three-dimensional representation of geometric data

3D computer graphics, sometimes called CGI, 3DCGI or three-dimensional computer graphics, are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images. The resulting images may be stored for viewing later or displayed in real time. Unlike 3D film and similar techniques, the result is two-dimensional, without the illusion of being solid.

Computer graphics Graphics created using computers

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 of specialized hardware and software has been developed, with the displays of most devices being driven by computer graphics hardware. It is a vast and recently developed area of computer science. The phrase was coined in 1960 by computer graphics researchers Verne Hudson and William Fetter of Boeing. It is often abbreviated as CG, or typically in the context of film as computer generated imagery (CGI). The non-artistic aspects of computer graphics are the subject of computer science research.

A vertex in computer graphics is a data structure that describes certain attributes, like the position of a point in 2D or 3D space, or multiple points on a surface.

Displacement mapping Computer graphics technique

Displacement mapping is an alternative computer graphics technique in contrast to bump mapping, normal mapping, and parallax mapping, using a (procedural-) texture- or height map to cause an effect where the actual geometric position of points over the textured surface are displaced, often along the local surface normal, according to the value the texture function evaluates to at each point on the surface. It gives surfaces a great sense of depth and detail, permitting in particular self-occlusion, self-shadowing and silhouettes; on the other hand, it is the most costly of this class of techniques owing to the large amount of additional geometry.

This is a glossary of terms relating to computer graphics.

References

  1. ↑ "Bump and Environment Mapping" (PDF). ics.uci.edu.
  2. 1 2 Blinn, James F. "Simulation of Wrinkled Surfaces", Computer Graphics, Vol. 12 (3), pp. 286-292 SIGGRAPH-ACM (August 1978)
  3. 1 2 Mikkelsen, Morten (2008). "Simulation of Wrinkled Surfaces Revisited" (PDF). p. 7 (Section 2.2). Archived (PDF) from the original on 2019-05-26. Retrieved 2011-08-05.
  4. ↑ Lengyel, Eric (July 2019). Foundations of Game Engine Development, Volume 2: Rendering. Terathon Software LLC. ISBN   978-0-9858117-5-4.
  5. ↑ Real-Time Bump Map Synthesis, Jan Kautz1, Wolfgang Heidrichy2 and Hans-Peter Seidel1, (1Max-Planck-Institut für Informatik, 2University of British Columbia)
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