Why convert BMP to PNG
This is the rare conversion on this bench that costs you nothing at all. BMP is a very old Windows format that writes out pixel values more or less as they are, with no meaningful compression. PNG is lossless too — every pixel comes back identical — but it actually compresses, and on the flat colour and repeated rows typical of BMP files it compresses very well indeed. The result is the same image, bit for bit as far as your eye and most software are concerned, usually somewhere between a half and a tenth of the size, in a format that every browser, phone and application made this century will open. If you have a BMP and you want it to stay exact, this is simply the better container for it.
What this conversion costs you
- Nothing visible, and in practice nothing at all. Both formats are lossless, so the pixels that come out are the pixels that went in. This is not a trade-off dressed up as one — it is a straight improvement in size and compatibility.
- Software older than about 1996 may not read PNG. Genuinely ancient systems that only understand BMP exist, mostly in industrial and scientific equipment. If you are converting a file *for* such a system rather than away from one, keep the BMP.
When not to do this
Avoid only if you do not actually need the image to stay lossless. If it is a photograph and nobody is going to edit it again, JPG is far smaller still — see <a href="../bmp-to-jpg/">BMP to JPG</a>, which typically cuts the size by 95 per cent. PNG is the right choice for screenshots, diagrams, artwork with flat colour, and anything with transparency.
Common questions
Is converting BMP to PNG lossless?
Yes, completely. Both formats store exact pixel values, so the image that comes out is identical to the one that went in. The only thing that changes is how efficiently those pixels are stored, which is why the file gets so much smaller with no visible difference whatsoever.
How much smaller will the PNG be?
It depends entirely on the picture. A screenshot or diagram with large areas of flat colour can shrink by ninety per cent or more, because PNG is very good at describing repetition. A detailed photograph saved as BMP might only halve. Either way it will be smaller, and never larger in any realistic case.
Why does anyone still have BMP files?
Older Windows software, some scanners, screen-capture tools and scientific or industrial instruments still write BMP because it is trivially simple to produce — there is no compression step to implement. It was never designed for storing or sharing images efficiently, which is why the files are so large.