BMP (Bitmap Image)
The format that taught Windows how to draw pictures on screen, one pixel at a time.
| Full name | Bitmap Image |
| Extension | .bmp |
| MIME type | image/bmp |
| Developer | Microsoft (with IBM for OS/2 variant) |
| Released | 1985 (Windows 1.0); revised 1987, 1990, 1995 |
| Type | Raster image |
| Color depth | 1, 4, 8, 16, 24, or 32 bits per pixel |
| Compression | Uncompressed (default) or RLE |
What is a BMP file?
BMP is a raster image format built into Microsoft Windows from the very beginning. It stores pixel data in a straightforward way, with no quality loss and minimal processing required to display it. Windows still uses BMP internally for icons, cursors, and wallpapers.
BMP stores images as a grid of pixels, each described by a fixed number of bits that represent its color. The format supports color depths from 1-bit black-and-white up to 32-bit true color with an alpha channel. Most BMP files are uncompressed, which means every pixel is stored exactly as-is with no transformation. An optional run-length encoding (RLE) mode exists for 4-bit and 8-bit images, but it is rarely used in practice.
History
Microsoft introduced BMP alongside Windows 1.0 in 1985 as a way to store device-independent bitmap data that could display correctly on different graphics hardware. The format was updated with Windows 2.0 in 1987 and significantly revised with Windows 3.0 in 1990 when Microsoft added the BITMAPINFOHEADER structure, which is still the most common header type today. Later revisions in Windows 95 and 98 added alpha channel support and ICC color profile embedding.
How it works
A BMP file starts with a 14-byte file header containing the magic bytes 'BM', the total file size, and the byte offset where pixel data begins. Immediately after comes an info header, most commonly the 40-byte BITMAPINFOHEADER, which stores image dimensions, color depth, compression type, and resolution. An optional color palette follows for indexed-color images (8-bit and below). Pixel rows are stored bottom-up by default and padded to a multiple of 4 bytes per row.
What it is used for
- Windows system graphics such as icons, cursors, and desktop wallpapers
- Intermediate format in image-editing pipelines where lossless, uncompressed data is needed
- Screen capture and paint applications that write raw pixel output without compression
- Printing workflows and legacy industrial software that require exact, unaltered pixel values
How to open it
Every version of Windows opens BMP files natively in Photos and Paint with no additional software. On Mac and Linux, Preview, GIMP, and most image editors read BMP without any plugins.
Pros and cons
Strengths
- Lossless by default: no compression artifacts, every pixel is stored exactly as captured
- Simple structure that every image library and operating system supports out of the box
- No patent or licensing restrictions on the format
- Fast to read and write because there is no encode or decode step for the pixel data
Trade-offs
- Very large file sizes compared to PNG, JPEG, or WebP for the same image
- No support for animation or multiple frames in a single file
- Poor web support: browsers accept BMP but it is almost never used on the web
- Bottom-up row storage and multiple header variants cause subtle compatibility issues in some decoders
Convert BMP files
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From BMP
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BMP FAQ
Why are BMP files so large?
BMP stores every pixel as raw color data with no compression by default. A 1920x1080 image at 24-bit color takes about 5.9 MB as a BMP, while the same image as a PNG might be under 1 MB. If file size matters, PNG gives you lossless compression with much smaller files.
Is BMP the same as DIB?
DIB stands for Device-Independent Bitmap, which is the internal Windows name for the same data structure. BMP is the file format on disk; DIB is the in-memory representation Windows uses when drawing. They describe the same pixel layout, so the terms are often used interchangeably.
Can I use BMP files on the web?
Technically yes, browsers can display BMP files, but almost nobody does. BMP files have no compression, so they load much slower than equivalent PNG or JPEG images. Use PNG for lossless graphics and JPEG or WebP for photographs.
What is the difference between BMP and PNG?
Both are lossless formats, but PNG uses DEFLATE compression to shrink file sizes by 50 to 80 percent without losing any image quality. PNG also supports transparency more cleanly and is universally supported on the web. BMP is simpler and faster to process but produces much larger files.