File Size: Why BMP Is So Large
A standard 24-bit BMP stores three bytes per pixel with no compression whatsoever. A 12-megapixel image (4000 × 3000 pixels) in BMP is approximately 34 MB- The same image as JPEG at quality 85 is around 3–5 MB. BMP files can be 5–20× larger than their JPEG equivalents depending on content complexity.
Colour Depth
BMP supports 1, 4, 8, 16, 24, and 32 bits per pixel. The most common variant is 24-bit (8 bits each for red, green, blue), which reproduces the same colour range as standard JPEG. 32-bit BMP adds an alpha channel, though alpha support in BMP viewers is inconsistent.
When BMP Is Still Required
- Windows wallpapers and system graphics in some legacy configurations
- Certain industrial and embedded systems whose firmware only reads raw bitmap data
- Older CAD and GIS applications with hard-coded BMP loaders
- Texture maps in some older game engines or toolchains
BMP vs Modern Formats
For virtually every modern use case, PNG is a superior alternative to BMP: PNG is lossless, supports transparency properly, and is typically 2–5× smaller than an uncompressed BMP. Convert BMP to JPEG when file size is the primary concern and lossless fidelity is not required.