.bmp File Extension

What kind of file is a .bmp?

A .bmp file is usually a Microsoft Windows Bitmap image. It stores a rectangular grid of pixels and normally uses the image/bmp MIME type. Most standalone BMP files begin with the bytes 42 4D, the ASCII letters BM. Check that signature when an image will not open, because changing another file's suffix to .bmp does not convert its contents.¹

BMP is a family of related binary layouts. A file header points to the pixel data, while an information header records dimensions, bit depth, compression, and color details. Common BMPs store pixels without compression, but indexed color, run-length compression, color profiles, and several header generations also exist.²

How do I open a .bmp on my computer?

• On Windows, open ordinary BMP images with Microsoft Paint, Photos, or a current web browser.
• On macOS, use a browser, GIMP, or Adobe Photoshop. Quick Look support can vary with the BMP variant.
• On Linux, use the desktop image viewer, GIMP, ImageMagick, or a browser.

Photoshop supports BMP and can save images with selectable bit depth and row order.³ If one application rejects a BMP, try an image editor with broader format support. Less common compression modes, color depths, or headers are not handled consistently by every decoder.

Poly support for .bmp

Poly recognizes .bmp filenames as images, creates thumbnails, opens decodable files in its image viewer, and indexes dimensions and available metadata. Visual search can find a BMP by its appearance, and the Poly agent can reason about the rendered image.

Text drawn into the pixels is not indexed as document text. Treat the file's extension as a hint rather than proof of its contents, especially when a download lacks the expected BM signature.

History of .bmp

Microsoft and IBM developed BMP in the 1980s for systems that needed to map raster graphics efficiently into memory. The format evolved from 16-bit to 32-bit structures and later gained additional color spaces, profiles, and compression choices.⁴

The three-letter .bmp suffix became the familiar filename convention on Windows. The standards-tree media type came much later: RFC 7903 registered image/bmp in 2016 and lists .bmp and .dib as associated extensions.¹⁴

Working with .bmp and alternatives

An uncompressed 24-bit BMP uses about three bytes per pixel, plus row padding and headers. A 1920 × 1080 image therefore needs about 5.93 MiB for its pixel data alone. That predictable layout is convenient for simple software, but inefficient for sharing or web delivery.

Choose the destination based on the image:

Converting an ordinary uncompressed BMP to PNG preserves its pixels and usually reduces the file size. JPEG can make a photograph smaller, but it discards detail. Keep the original until you have checked color, transparency, and compatibility in the converted copy. For widest BMP interoperability with older tools, a conventional uncompressed 24-bit export is often the safest choice.