What is a BMP file?
BMP — Windows bitmap
What is it?
BMP stores an image pixel by pixel, with no compression whatsoever: every dot in the image takes up its full share of space in the file. The result is utterly simple — and unreasonably heavy.
A 1920 by 1080 image weighs in at roughly 6 MB as a BMP, compared to 300 KB as a JPEG for a result that looks identical to the eye.
History & origin
BMP dates back to the earliest versions of Windows, in the late 1980s. Computing power was scarce at the time, and it made more sense to spend disk space than processor time: skipping compression altogether was a rational choice.
That trade-off no longer makes any sense today, and the format only survives out of inertia, in old software and a handful of technical uses.
Why it is useful
Total simplicity: no decoding, no artifacts, no loss. Any program can read a BMP with just a few lines of code.
It still has its uses in certain embedded or industrial settings, where simplicity matters more than file size.
Limits & drawbacks
An indefensible file size, with no quality advantage over PNG, which is also lossless yet ten times lighter.
No reliable transparency, no support on the web, no metadata.
Practical tips
There's no longer any reason to keep a BMP file. Convert it to PNG: you'll keep the exact same lossless quality for a fraction of the size.
If it's a photo, JPEG will be even lighter, at the cost of lossy compression that's practically invisible in real-world use.
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