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Normal mapping used to re-detail simplified meshes.
Normal mapping used to re-detail simplified meshes.

In 3D computer graphics, normal mapping is an application of the technique known as bump mapping. 3D computer graphics (in contrast to 2D computer graphics) are graphics that use a three-dimensional representation of geometric data that is stored in the computer ' Bump mapping' is a Computer graphics technique where at each Pixel, a perturbation to the Surface normal of the object being rendered is Normal mapping is sometimes referred to as "Dot3 bump mapping". While bump mapping perturbs the existing normal (the way the surface is facing) of a model, normal mapping replaces the normal entirely. Like bump mapping, it is used to add details to shading without using more polygons. Shading refers to depicting depth in 3D models or illustrations by varying levels of Darkness. In 3D computer graphics, polygonal modeling is an approach for modeling objects by representing or approximating their Surfaces using Polygons Polygonal But where a bump map is usually calculated based on a single-channel (interpreted as grayscale) image, the source for the normals in normal mapping is usually a multichannel image (x, y and z channels) derived from a set of more detailed versions of the objects. In Computing, a grayscale or greyscale Digital image is an image in which the value of each Pixel The values of each channel usually represent the xyz coordinates of the normal in the point corresponding to that texel. A texel, or tex ture el ement (also tex ture pi' xel) is the fundamental unit of texture space used in Computer graphics

Normal mapping is usually found in two varieties: object-space and tangent-space normal mapping. They differ in coordinate systems in which the normals are measured and stored.

One of the most interesting uses of this technique is to greatly enhance the appearance of a low poly model exploiting a normal map coming from a high resolution model. Low poly is a term used by videogame creators players and journalists alike to describe a three-dimensional computer generated character or object that appears to be lacking in polygons While this idea of taking geometric details from a high resolution model had been introduced in "Fitting Smooth Surfaces to Dense Polygon Meshes" by Krishnamurthy and Levoy, Proc. SIGGRAPH 1996, where this approach was used for creating displacement maps over nurbs, its application to more common triangle meshes came later. SIGGRAPH (short for S pecial I nterest G roup on GRAPH ics and Interactive Techniques is the name of the annual conference on Computer graphics Displacement mapping is an alternative computer graphics technique in contrast to Bump mapping, Normal mapping, and Parallax mapping, using a ( procedural Non-uniform rational B-spline ( NURBS) is a mathematical model commonly used in Computer graphics for generating and representing curves and surfaces In 1998 two papers were presented with the idea of transferring details as normal maps from high to low poly meshes: "Appearance Preserving Simplification", by Cohen et al. SIGGRAPH 1998, and "A general method for recovering attribute values on simplified meshes" by Cignoni et al. IEEE Visualization '98. The former presented a particular constrained simplification algorithm that during the simplification process tracks how the lost details should be mapped over the simplified mesh. The latter presented a simpler approach that decouples the high and low polygonal mesh and allows the recreation of the lost details in a way that is not dependent on how the low model was created. This latter approach (with some minor variations) is still the one used by most of the currently available tools.

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How it works

To calculate the Lambertian (diffuse) lighting of a surface, the unit vector from the shading point to the light source is dotted with the unit vector normal to that surface, and the result is the intensity of the light on that surface. See also Lambert's cosine law If a surface exhibits Lambertian reflectance, light falling on it is scattered such that the apparent brightness of the surface to an observer In Mathematics, the dot product, also known as the scalar product, is an operation which takes two vectors over the Real numbers R Imagine a polygonal model of a sphere - you can only approximate the shape of the surface. By using a 3-channel bitmap textured across the model, more detailed normal vector information can be encoded. Each channel in the bitmap corresponds to a spatial dimension (X, Y and Z). These spatial dimensions are relative to a constant coordinate system for object-space normal maps, or to a smoothly varying coordinate system (based on the derivatives of position with respect to texture coordinates) in the case of tangent-space normal maps. This adds much more detail to the surface of a model, especially in conjunction with advanced lighting techniques.

Normal mapping in videogames

Interactive normal map rendering was originally only possible on PixelFlow, a parallel graphics machine built at the University of North Carolina at Chapel Hill. The University of North Carolina at Chapel Hill ( UNC, North Carolina, or simply Carolina) is a public, Coeducational Research It was later possible to perform normal mapping on high-end SGI workstations using multi-pass rendering and frame buffer operations or on low end PC hardware with some tricks using paletted textures. Silicon Graphics Inc (commonly initialised to SGI, historically sometimes referred to as Silicon Graphics Computer Systems or SGCS) is a company However, with the advent of shaders in home PCs and gaming consoles, normal mapping became widely used in proprietary commercial videogames starting in late 2003, and followed by open source games in later years. A shader in the field of Computer graphics is a set of software instructions which is used by the graphic resources primarily to perform rendering effects The word proprietary indicates that a party or proprietor exercises private Ownership, control or use over an item of Property. Commerce is a division of trade or production which deals with the exchange of goods and services from producer to final consumer Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. Normal mapping's popularity for real-time rendering is due to its good quality to processing requirements ratio versus other methods of producing similar effects. Much of this efficiency is made possible by distance-indexed detail scaling, a technique which selectively decreases the detail of the normal map of a given texture (cf. mipmapping), meaning that more distant surfaces require less complex lighting simulation. In 3D computer graphics Texture filtering, MIP maps (also mipmaps) are pre-calculated optimized collections of bitmap images that

Microsoft's Xbox was the first home game console to support the effect on the GPU (other sixth generation consoles use a CPU-based implementation). The Xbox is a sixth-generation Video game console produced by Microsoft Corporation. The sixth-generation era (sometimes referred to as the 128-bit era; see "Number of bits" below refers to the computer and Video games Developers on the Xbox 360 and the PlayStation 3 rely heavily on normal mapping and are beginning to implement parallax mapping. The Xbox 360 is the second Video game console produced by Microsoft, and was developed in cooperation with IBM, ATI, and SiS. Parallax mapping (also called offset mapping or virtual displacement mapping) is an enhancement of the Bump mapping or Normal mapping techniques

See also

External links

Bibliography

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