File extension

.bmp

Windows Bitmap (BMP/DIB)

.bmp is primarily used for Windows and OS/2 bitmap images: simple raster files built around DIB headers, optional palettes, and mostly uncompressed pixel data.

Known meanings

Formats and reference material for .bmp

Windows Bitmap (BMP/DIB)

Raster bitmap image format using a BMP file header plus a device-independent bitmap header

  • windows 2d-graphics
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OS/2 Bitmap format

OS/2 Bitmap format

  • 2d-graphics
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The .bmp file format

Historical BMP file format reference

  • windows 2d-graphics
  • Stefan Hetzl
  • Historical
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Windows Bitmap-File Addendum

Windows Bitmap-File Addendum

  • windows 2d-graphics
  • Kevin D. Quitt
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Windows BMP Format

Windows BMP Format (MS Word)

  • windows 2d-graphics
  • Wim Wouters
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Details

Format notes

Windows Bitmap (BMP/DIB)

BMP is a family of raster bitmap formats associated with Microsoft Windows and OS/2. The common Windows file form starts with a bitmap file header, followed by a DIB header, optional color masks or palette entries, and the pixel array. The format is easy to parse for common files, but real-world compatibility depends on which DIB header variant and compression mode a file uses.

Headers And Variants

The first two bytes of a normal BMP file are BM. The file header records the offset to pixel data, while the DIB header describes width, height, planes, bit depth, compression, image size, resolution, palette usage, and sometimes color masks or color-space metadata. Older OS/2 files use smaller core headers; Windows files commonly use BITMAPINFOHEADER or later extended headers.

Pixel Layout

Classic BMP scan lines are padded to a DWORD/LONG boundary. Positive heights normally store rows bottom-up, while negative heights indicate top-down storage. Indexed color files use a palette. Truecolor Windows BMP files commonly store 24-bit pixels as BGR byte triples. For 16-bit and 32-bit images, channel interpretation may be implied by the compression mode or defined explicitly with BI_BITFIELDS masks.

Compression And Preservation Notes

Many BMP files use BI_RGB, meaning uncompressed pixel data. Other modes include run-length encoding for 4-bit and 8-bit images and bitfield masks. Newer variants can use JPEG or PNG payload identifiers, but these are not widely interoperable as ordinary standalone BMP files. Preservation checks should record header type, dimensions, bit depth, compression mode, palette length, row stride, and whether alpha data is meaningful for the target reader.

Security Notes

BMP parsers should validate dimensions, row-stride arithmetic, palette sizes, pixel offsets, and compressed stream bounds. Large dimensions or crafted header values can trigger integer overflow, excessive allocation, or out-of-bounds reads in naive decoders.