3D games use textures to add realism to the environment, creating walls, floors, ceilings, or whatever geometric form is required. To enhance realism, methods were developed to add lighting effects to the textures, and in Unreal and Quake a separate lighting map was generated for each level. What the user experienced, was a result of rendering and merging two maps.

Bump mapping took texture lighting one stage further, and added height information to the lighting map, so a sense of depth could be added to textures when looking directly at them. A gargoyle face would be less lit in the eye sockets for example. Finally normal maps were developed, that contained x,y,z co-ordinate information about lighting, allowing a precision in light rendering, not allowed by bump mapping. For example, the gargoyle could now be lit by a flickering torch placed at its lower left side.

With this the increased level of complexity seen in normal lighting maps, what had been originally simple enhancements to the main textures, began to take up much more space. S3TC could not be applied to normal maps, because the lighting information has to be applied precisely, or a significant drop in visual quality is apparent.

With this in mind, 3Dc was developed by ATI as an enhancement of the DXT5 standard, to enable detailed lighting effects, while minimizing memory usage. It features up to 4:1 compression, allowing designers to quadruple lighting map detail, without requiring either more memory or bandwidth.

Although 3Dc was formally introduced with the ATI x800 series cards, there is also an S3TC compatible version planned for the older R3xx series, and cards from other companies. The quality and compression will not be as good, but the visual errors will still be significantly less than offered by standard S3TC.

References

• What is a Normal Map?
• CREATING AND USING NORMAL MAPS
• Creating Normal Maps
• 3Dc - higher quality textures with better compression