3Dc

3Dc (FourCC : ATI2), also known as DXN, BC5, or Block Compression 5 is a lossy data compression algorithm for normal maps invented and first implemented by ATI. It builds upon the earlier DXT5 algorithm and is an open standard. 3Dc is now implemented by both ATI and Nvidia.

== Target application == The target application, normal mapping, is an extension of bump mapping that simulates lighting on geometric surfaces by reading surface normals from a rectilinear grid analogous to a texture map - giving simple models the impression of increased complexity. This additional channel however increases the load on the graphics system's memory bandwidth. Pre-existing lossy compression algorithms implemented on consumer 3D hardware lacked the precision necessary for reproducing normal maps without excessive visible artefacts, justifying the development of 3Dc.