Convert bmp to dds Online: bmp2dds
You can use Tom's Editor to easily convert images from
Microsoft Windows bitmap .BMP to Direct Show Surface
Tom's Editor is a free, online image manipulation and converter program.
Go to Tom's Editor
Format created by Microsoft for their Windows and OS/2 operating systems. Images can be compressed or not.
DDS are files invented by Microsoft to be used in games, mostly as textures. Images can be compressed to save space but the compression methods defined by DDS are all very fast in terms of coding and decoding.