From bitmap to PNG without any quality loss
BMP (Windows bitmap) is one of the oldest image formats still in use. Most BMP files store raw pixel values with no compression at all, which makes them simple but enormous. PNG is also lossless, but it compresses pixel data with the DEFLATE algorithm. Converting BMP to PNG therefore keeps every pixel exactly as it was while cutting the file size dramatically.
How much smaller?
An uncompressed 24-bit BMP needs three bytes per pixel. A 1920 × 1080 image is therefore about 6.2 MB no matter what it shows. As a PNG, the same screenshot is often a few hundred kilobytes, and a simple diagram with large flat areas can be smaller still. Photos compress less well, but PNG is still typically much smaller than the BMP. The converter shows the exact before and after sizes.
Why convert BMP files?
- Web publishing. Browsers can display BMP, but CMSs, forums and social networks often reject it, and page load times suffer.
- Email and chat. Smaller attachments send faster and stay under size limits.
- Archiving old files. Scans, clip art and screenshots from older Windows programs are frequently BMPs; PNG preserves them losslessly in a modern format.
- Documentation. Screenshots exported by legacy tools or embedded systems can be converted for use in wikis and README files.
PNG vs BMP
| BMP | PNG | |
|---|---|---|
| Quality | Lossless | Lossless |
| Compression | Usually none | DEFLATE, typically much smaller |
| Transparency | Rarely supported by software | Full alpha channel, widely supported |
| Web support | Poor for uploads | Universal |
Is PNG always the right replacement?
For screenshots, diagrams, icons and scanned documents, yes. For large photographs that only need to look good on screen, a JPG or WebP will be smaller still, at the cost of being lossy.
Technical notes
The converter reads any BMP your browser can decode, including 1-, 4-, 8-, 24- and 32-bit files and the .dib extension. The output is a standard PNG with the same dimensions. If the bitmap contains alpha information that your browser understands, it is preserved; otherwise the image is fully opaque.
Want an even smaller file for the web? The BMP to JPG converter is best for photographs. Need BMP again later, for example for legacy software? Use PNG to BMP. To reduce the dimensions as well, try the image resizer.
The image is decoded and re-encoded by your own browser using the canvas API. It is never uploaded, so private photos and screenshots stay on your device.
Converting many bitmaps at once
This page is ideal for a handful of files. If you have a folder of hundreds, a command-line tool does the same lossless conversion in one go:
# ImageMagick: convert every BMP in the folder to PNG
magick mogrify -format png *.bmp
# Python with Pillow
from PIL import Image
Image.open("scan.bmp").save("scan.png", optimize=True)Whichever route you choose, compare a converted file with the original at 100% zoom before deleting the bitmaps. Because PNG is lossless the pixels should be identical; if colors look different, the BMP probably used an unusual header or color profile that the decoder did not understand.