Efficient bump mapping using height maps

Abstract

A method for generating bump map data substantially in real time for use in a 3-dimensional computer graphics system. Data is received which defines an area to which a texture is to be applied. Texture data to apply to the area is also received. This data includes surface height data. A set of partially overlapping samples of texture data are then filtered and surface tangent vectors derived therefrom. A bump map surface normal is then derived from the tangent vectors.

Description

[0001] This invention relates to a method and apparatus for generating bump map data for use in a 3 dimensional computer graphics system.BACKGROUND TO THE INVENTION[0002] In the field of 3D computer graphics, detail is often added to otherwise smooth objects though the use of Bump Mapping, which was introduced by Blinn in his paper "Simulation of Wrinkled Surfaces" (SIGGRAPH 1978, pp286-292). This operates by perturbing, on a pixel-by-pixel basis, an object's otherwise `smoothly` varying surface normal vector. Because the surface's normal vector is used when computing the shading of that surface, its modification can give the appearance of bumps. FIG. 1 shows a surface normal being perturbed.[0003] In Blinn's technique, each perturbation is computed by first taking derivates of a bump displacement texture or `height map` and subsequently applying it to the original surface normal and surface tangent vectors. The height map is a simple array of scalar values that gives the `vertical`...

AI Technical Summary

Problems solved by technology

Unfortunately many of the commonly used texture compression schemes are not suitable as they cause a loss of information that, when applied to the special case of normal maps, can cause an unacceptable degradation in image quality.

Problems can arise, however, when applying the texture filtering techniques, e.g. bilinear or trilinear filtering, to normal maps.

Unfortunately, the human visual system is very sensitive to changes in the derivative of image intensity, and so `artefacts` can be seen.

The `large` texture formats consume valuable bandwidth as well as memory and cache storage and, although special normal map compression techniques exist, these formats are still often larger than the original source height map.

Also filtering of the normal map may also be problematic.

A further limitation of Peercy et al's technique is that dynamic bump mapping, i.e. where the bump heights are computed frame-by-frame, is far more difficult to achieve.

The pre-processing step, including generation of the various MIP map levels, may take too much time to allow real-time rendering.

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