{
  "id": "magic/bmp",
  "family": "magic",
  "slug": "bmp",
  "title": "BMP signature (BM)",
  "summary": "A Windows bitmap (BMP) file begins with the 2-byte ASCII signature 'BM' (0x42 0x4D), followed by a 4-byte little-endian total file size. 'BM' is by far the most common of several possible bitmap-type marks.",
  "kind": "signature",
  "aliases": [
    "BMP magic",
    "bitmap",
    "BM"
  ],
  "status": "de-facto",
  "verification": "verified",
  "tier": "B",
  "source_url": "https://learn.microsoft.com/en-us/windows/win32/api/wingdi/ns-wingdi-bitmapfileheader",
  "source_version": "Microsoft BITMAPFILEHEADER (bfType 0x4D42 = 'BM')",
  "retrieved_date": "2026-05-29",
  "see_also": [
    "magic/ico",
    "magic/png"
  ],
  "ext_type": "file-signature@1",
  "ext": {
    "magic_hex": "42 4D",
    "offset": 0,
    "magic_ascii": "BM",
    "extensions": [
      "bmp",
      "dib"
    ],
    "mime": "image/bmp",
    "spec": "Microsoft BITMAPFILEHEADER",
    "notes": [
      "bfType is the 16-bit value 0x4D42 stored little-endian => bytes 42 4D = 'BM'.",
      "Bytes 2-5: bfSize, total file size in bytes, little-endian.",
      "Bytes 10-13: bfOffBits, offset to the pixel array.",
      "Rare alternative type marks ('BA','CI','CP','IC','PT') come from OS/2 and are essentially never seen."
    ]
  },
  "updated": "2026-05-29T00:00:00Z"
}