BMP
The native Windows raster format storing pixel data uncompressed. Fast to read/write but produces very large files.
BMP (Bitmap Image File) is a raster image format designed by Microsoft for the Windows operating system. It stores pixel color data essentially uncompressed, enabling extremely fast read and write operations at the cost of significantly larger file sizes compared to compressed formats.
The file structure consists of a header section and pixel data section. The header contains metadata such as image dimensions, color depth, and compression method. Pixel data is typically stored in bottom-up scanline order, from the lowest row to the highest.
- Color depth: Supports 1-bit (monochrome), 4-bit (16 colors), 8-bit (256 colors), 16-bit, 24-bit (true color), and 32-bit (with alpha channel)
- RLE compression: Optional Run-Length Encoding is available but rarely used in practice
- DIB compatibility: Direct compatibility with Windows GDI (Graphics Device Interface) enables fast rendering to device contexts
BMP is unsuitable for web delivery due to its large file sizes, but it serves important roles as an intermediate format in image processing pipelines, temporary storage for screen captures, and framebuffer output in embedded systems where compression overhead must be avoided. Virtually every image library supports BMP, including Python's Pillow and C's stb_image, making it a reliable lowest-common-denominator format for cross-platform development.