BMP is the Windows bitmap: pixel values written out with essentially no compression, which makes the files enormous and the format trivial to read. It survives in Windows tooling, embedded systems and anywhere a program wants image data without a decoder in front of it. Rows are stored bottom-up.
Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop a BMP file above and choose afterwards.