BMP File Format (.bmp)

A BMP file holds a device-independent bitmap: a pixel grid stored with a Microsoft-defined header and, in the overwhelming majority of BMP files in the wild, no compression at all.

.bmpImage Files

BMP at a glance#

Full name	Microsoft Windows bitmap image
File extension	.bmp
Category	Image Files
Developer	Microsoft
MIME types	image/bmpimage/x-bmp
Other extensions	.dib
Compression	Varies from file to file
Specification	Microsoft Bitmap Storage / DIB header documentation
FileFlip support	FileFlip reads and writes this format

What a .bmp file can hold#

These are the things a BMP file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.

Transparency (alpha channel)	Yes
Animation	No
Lossless compression	Yes
Embedded metadata	No
Colour profiles	Yes
High dynamic range	No

Strengths and limitations of BMP#

What BMP does well

Pixel data is stored exactly as-is by default, so there is zero generational quality loss from re-saving
Trivial to decode, which is why it's a common intermediate format for image-processing tools and screenshot utilities
Supports color depths from 1-bit monochrome up to 32-bit with alpha, more range than GIF's 8-bit palette
The newer V5 header can embed an ICC color profile directly in the file

Where BMP falls short

Uncompressed BMP files run many times larger than a PNG or JPEG of the same image, since no space-saving encoding is applied
Its run-length compression modes (RLE4, RLE8) only work on 4-bit and 8-bit palette images, not on 24-bit or 32-bit photos
The alpha channel added in the V4 and V5 headers is widely ignored by viewers and browsers, so transparency often doesn't survive being opened elsewhere
Almost never used on the web, since every browser-native alternative compresses far better

Use BMP when a Windows-native application, printer driver, or legacy tool specifically expects it, or when pixel data has to be stored with zero encoding overhead for a processing pipeline.

Convert BMP to PNG or JPEG for anything leaving that pipeline, since both produce a far smaller file and PNG matches BMP's lossless, generation-safe quality.

How to open a .bmp file#

A .bmp file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts BMP into a format your machine already opens, and it does it in the browser tab rather than on a server.

Platform	Programs that open it
Windows	Photos, Paint, Adobe Photoshop, IrfanView, GIMP
macOS	Preview, Adobe Photoshop, GIMP, Affinity Photo
Linux	GIMP, Eye of GNOME, ImageMagick
iOS	Files
Android	Google Photos, Gallery
Web	FileFlip

BMP questions people ask#

Why are BMP files so much bigger than JPEG or PNG?

Most BMP files store every pixel's color value directly with no compression, so a BMP is close in size to the raw uncompressed image data. JPEG and PNG both apply compression, lossy in JPEG's case and lossless in PNG's, which is why the same photo saved as either is a fraction of the size of a BMP.

Can a BMP file be compressed?

Yes, though it's rare in practice. The BMP specification includes run-length encoding modes, RLE8 for 8-bit images and RLE4 for 4-bit images, that compress losslessly the same way GIF's LZW does, just less efficiently. Almost all BMP files encountered in practice still use BI_RGB, the uncompressed mode, because that is what most software defaults to writing.

Does BMP support transparency?

It can, but support is inconsistent. The BITMAPV4HEADER and BITMAPV5HEADER, both extensions to the original format, can store a 32-bit image with an alpha channel, but many image viewers, browsers, and older software ignore that alpha data entirely and render the image as fully opaque. PNG's alpha transparency is much more reliably supported across software.

Is BMP the same thing as a DIB?

They're closely related. DIB, device-independent bitmap, is the internal Windows data structure of header, color table, and pixel data that a BMP file wraps in a short file header. The .dib extension is used for that same data saved without expecting the .bmp file header, which is why BMP and DIB are treated as aliases of the same format.

Why does old Windows software still use BMP?

BMP has been part of the Windows GDI graphics API since the 1980s, so decades of Windows applications, printer drivers, and icon or wallpaper tools were built to read and write it natively without needing an external image library. That built-in support, plus the format's simplicity to decode, is why it has stayed in use in Windows-specific tooling even though it's a poor choice for sharing images.

Converting BMP files#

Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.