BMP vs PNG
Use PNG. Both are lossless, so they look identical, but BMP stores pixels almost uncompressed and is often several times the size of the same image as PNG. BMP only makes sense for old software that reads nothing else.
Last updated
Choose BMP when
- Old Windows software or embedded devices that read nothing else.
- Tools that want raw, uncompressed pixels.
Choose PNG when
- Everything else: screenshots, graphics, any image you keep or share.
- Anything that needs transparency, which BMP rarely supports in practice.
What BMP actually is
BMP stores pixels as a plain array with a small header, and in its usual form applies no compression at all. That makes it very simple to read and write, and very large: a 4000 by 3000 photograph is about 48 MB regardless of what is in it.
The file size surprises people. There is no compression to speak of, so the size depends only on the dimensions, not on how complicated the image is.
What PNG actually is
PNG stores every pixel exactly as it was, using a compression method that throws nothing away. It carries a full alpha channel, so a pixel can be any degree of transparent rather than simply on or off, and it handles up to 16 bits per colour channel.
People save photographs as PNG and wonder why an email bounces. A photo that is 400 KB as a JPG is routinely 4 MB as a PNG, because lossless compression cannot do much with the noise in a real photograph.
BMP and PNG side by side
| BMP | PNG | |
|---|---|---|
| Extension | .bmp | .png |
| Media type | image/bmp | image/png |
| Compression | Lossless | Lossless |
| Transparency | Yes | Yes |
| Animation | No | No |
| Quality setting | Not applicable | Not applicable |
| We can write it | Yes | Yes |
Questions
Does converting BMP to PNG lose quality?
No. Both are lossless, so every pixel stays the same; only the file gets smaller.
Why are BMP files so big?
A BMP usually stores every pixel as three or four bytes with no compression, so a 12-megapixel image is about 36 MB whatever it shows.