The BMP format
Essentially raw pixels in a file. Simple, huge, and almost never the right choice today.
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BMP とは？
BMP is Microsoft’s bitmap format, storing pixels largely uncompressed. A 1920 × 1080 image at 24 bits per pixel is about 6 MB regardless of content — the same photo as a JPEG might be 300 KB.
That simplicity was the point. Decoding a BMP requires almost no computation, which mattered a great deal in the late 1980s and matters not at all now.
You still encounter BMPs from older Windows software, some scanner drivers, and certain scientific and industrial tools where the format’s predictability is worth the size.
主な用途
- Output from legacy Windows applications
- Some scanner and capture-card drivers
- Intermediate files where decode simplicity matters more than size
長所
- Trivially simple to read and write
- Lossless — no compression artefacts at all
- Long-standing Windows support
短所
- Enormous files with no practical compression
- No animation and inconsistent transparency support
- Poor support on the web — most sites will reject it
- No advantage over PNG, which is also lossless and far smaller
ブラウザ対応状況
Most browsers can display BMP, but it should not be used on the web. Convert to PNG for a lossless equivalent, or JPEG/WebP for a photograph.