BMP bitmap BMP was developed by Microsoft and is the native graphics format for Windows users. The images you see when Windows starts up and closes, and the wallpaper that adorns your desktop, are all in BMP format. BMP tends to store graphical data inefficiently, so the files it creates are larger than they need to be. But at least wallpaper file sizes can be reduced using a technique called run-length encoding. See also: run-length encoding