Convert BMP to PNG

BMP is the bitmap format Windows Paint saved by default for decades, and it is still what some scanners, CNC and embroidery programs, microscope cameras and old industrial software write out. It stores every pixel raw, row by row, so a 1920 by 1080 screenshot takes about 6 MB whether it shows a photo or a blank page. Many upload forms, chat apps and content systems reject it outright.

PNG is the natural replacement because it is also lossless. The colours of every pixel in the PNG match the bitmap exactly, but PNG compresses runs of repeated colour, so a diagram, screenshot or pixel-art sprite typically shrinks to a tenth of the BMP or less. Photos saved as BMP shrink less, often by half.

Your browser reads the bitmap, including the 1, 4 and 8-bit palette variants and 32-bit files with an alpha channel, and writes the PNG inside this tab. Nothing is sent to a server, which matters when the bitmaps come from lab equipment, medical imaging or a client’s scanner.

A few practical notes on specific sources. Screenshots saved from very old versions of Windows Paint, and exports from tools like MS Paint on Windows XP, are 24-bit and convert cleanly. Bitmaps from embroidery and sign-cutting software are often 1-bit or 4-bit with a tiny palette; the PNG keeps those exact colours, and is usually a few kilobytes. Game textures and sprite sheets from older engines sometimes use a magenta or bright green key colour instead of real transparency: that colour is kept as a normal colour, so remove it in an image editor if you need a transparent PNG.

If you are converting a folder of bitmaps for a website or an archive, drop them all at once and download the zip. File names stay the same apart from the extension, so links and references are easy to update. For photographs where size matters more than perfection, JPG gets much smaller still.

Why not just rename the file? Changing .bmp to .png leaves the bytes untouched, so the file still starts with the BM signature and stays the same size. Some viewers sniff the contents and open it anyway, but upload forms, content management systems and image hosts check the signature and refuse it, or worse, accept it and show a broken image later. A real conversion rewrites the data in PNG form.