S3 Texture Compression
S3TC Format Comparison
Columns: FOURCC | DX 10 Name | Description | Alpha premultiplied? | Compression ratio | Texture Type
DXT1 | BC1 | 1-bit Alpha / Opaque | N/A | 6:1(for 24 bit source image) | Simple non-alpha | DXT2 | (none) | Explicit alpha | Yes | 4:1 | Sharp alpha | DXT3 | BC2 | Explicit alpha | No | 4:1 | Sharp alpha | DXT4 | (none) | Interpolated alpha | Yes | 4:1 | Gradient alpha | DXT5 | BC3 | Interpolated alpha | No | 4:1 | Gradient alpha