BMP File Format (Bitmap Image File)
BMP (Bitmap) is one of the simplest raster image formats, developed by Microsoft for Windows. BMP files store pixel data with minimal or no compression, resulting in very large files that preserve every pixel exactly. The format was originally designed for the Windows GDI (Graphics Device Interface) and remains the native image format for many Windows system operations. BMP supports various color depths from 1-bit monochrome to 32-bit with alpha channel. While BMP is rarely used for web or modern workflows due to its large file sizes, it is still encountered in legacy systems, embedded applications, and scenarios where uncompressed pixel data is required.
Quick Facts
- Extension: .bmp
- MIME Type: image/bmp
- Category: image
Advantages
- Lossless with zero compression artifacts
- Simple format that is easy to read and write programmatically
- Native Windows support without any codec requirements
- Predictable file sizes based on dimensions and bit depth
- Good for temporary storage during image processing pipelines
Disadvantages
- Extremely large file sizes due to minimal compression
- Not suitable for web use
- Limited metadata support
- No animation capability
- Outdated for modern image workflows
Common Use Cases
- Legacy Windows application compatibility
- Embedded systems and hardware interfaces
- Temporary intermediate format in image processing
- Simple graphics in older software systems
- Raw pixel data storage for scientific imaging
Technical Details
BMP files consist of a file header (14 bytes), an info header (40+ bytes for BITMAPINFOHEADER), an optional color table, and raw pixel data. Pixel rows are stored bottom-to-top by default and padded to 4-byte boundaries. Optional RLE (Run-Length Encoding) compression is available for 4-bit and 8-bit images but rarely used. The DIB (Device Independent Bitmap) header supports various versions: BITMAPCOREHEADER, BITMAPINFOHEADER, BITMAPV4HEADER, and BITMAPV5HEADER, each adding color management and transparency features.
Frequently Asked Questions about BMP
Why are BMP files so large?
BMP stores pixel data with little to no compression. A 1920x1080 24-bit BMP is approximately 6 MB, while the same image as JPG might be 200 KB.
Should I use BMP for anything?
BMP is mostly used in legacy systems, embedded applications, and as an intermediate format in image processing. For everyday use, JPG, PNG, or WebP are better choices.
Can BMP files have transparency?
Yes, 32-bit BMP files include an alpha channel for transparency, though support varies across applications.
How do I convert BMP to a smaller format?
Convert to JPG for photographs (60-80% size reduction) or PNG for graphics with transparency. WebP provides the best compression for web use.