What is GIF?
GIF is thirty-eight years old and refuses to die, because it animates and everything opens it. The cost is its palette: 256 colours per frame, so photographs come out visibly banded. Transparency is on-or-off per pixel, with no partial opacity.
What is BMP?
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.