Convert BMP to PNG

Why BMP files are so big

A bitmap file is essentially a raw dump of pixel values. A 1,920 by 1,080 image at 24 bits per pixel is a little over 6 MB, every time, whether it is a complex photograph or a solid blue rectangle. There is no clever encoding, no run-length shortening, nothing. That simplicity is useful for old hardware and software, but it makes BMP a poor choice for storing, sending or publishing images.

Why PNG is the natural upgrade

PNG is also lossless, which means the conversion keeps every pixel exactly. But PNG runs the pixel data through a prediction filter and DEFLATE compression, the same algorithm used in ZIP files. Areas of flat colour, repeated patterns and gradual gradients shrink enormously. That same 6 MB screenshot as a BMP is often 200 to 400 KB as a PNG. Photographs with a lot of fine detail compress less, but still usually end up at half the size or smaller.

If the BMP is a photograph and you do not need lossless storage, converting to JPG or WebP instead will produce a far smaller file again. Use PNG when you want a perfect copy.

Where BMPs usually come from

• Screenshots and exports from older Windows programs and Paint.
• Output from scanners, medical or scientific instruments and industrial cameras.
• Game and application assets from older software.
• Files extracted from embedded devices or firmware.
• Old CD-ROMs and archives.

After conversion

The PNG is a drop-in replacement in every modern context: it can be attached to email, uploaded to any website, embedded in a document or placed in a design layout. PNG also supports transparency, so if your BMP has a background you want to remove, you can now do that in an editor and keep the result transparent. Drop a whole folder of BMPs in at once and download the PNGs as a single ZIP.