Where BMP came from
BMP arrived with Windows 2.0 in 1987 as the operating system's native raster format. It stores pixels raw with essentially no compression, which made it fast to blit on 1980s hardware and makes it enormous today. It survives in places where simplicity beats efficiency: industrial controllers, medical imaging stations, scientific instruments, CNC and embedded software whose image loader was written once and never revisited.
The technical picture
Compression: None — three uncompressed bytes per pixel. Transparency: Technically in 32-bit mode; most software ignores it. Animation: Not supported. Colour: 8-bit per channel. Typical file size relative to WebP: 15-40x larger than WebP — a 2 MB WebP becomes a 35 MB BMP.
Where it opens
Universal, but rarely the preferred format anywhere. This is usually the deciding factor when choosing between BMP and WebP — WebP renders in every browser but is uneven in desktop software, while BMP has a very different support profile.
Converting BMP to WebP
BMP's total lack of compression makes it painful to store or move. Converting to WebP typically cuts 95% or more off the file with no visible change, which is why BMP archives are among the biggest wins this converter produces. Plan for the size: BMP output is roughly width x height x 3 bytes regardless of what the picture contains. Resize before converting if the destination caps file size.
Converting WebP to BMP
Convert WebP to BMP when the destination is a machine rather than a person — legacy Windows software, industrial control panels, lab instruments and embedded systems that accept uncompressed bitmaps and nothing else. None of them have any idea what a WebP is. Expect the BMP output to be 15-40x larger than WebP — a 2 MB WebP becomes a 35 MB BMP — that difference is the price of getting a format the destination will actually accept.