BMP to PNG

BMP to PNG is a free tool that converts bitmap image files into compressed PNG files entirely in your browser.

How do I convert a BMP file to PNG?

Add the BMP image, allow the browser to process it, then save the resulting PNG file. The image is never uploaded to a server because all conversion work takes place in your browser.

1. Provide the BMP file you want to convert.
2. Wait while the browser decodes the bitmap and encodes the pixels as PNG.
3. Save the PNG and open it to check its colours, dimensions and transparency.

Browser-based BMP-to-PNG processing keeps the source BMP on your device. This can matter for BMP scans, internal diagrams and other bitmap files that should not be sent to a third-party conversion server.

What changes when BMP is converted to PNG?

The pixel data is stored using PNG's lossless compression instead of BMP's usually uncompressed bitmap structure. The conversion changes the file format rather than adding detail or increasing the image resolution.

Converting a BMP does not automatically make a background transparent. If the BMP contains white background pixels, those pixels remain white unless an image editor removes them. A single-frame BMP also cannot provide frames for an animated PNG.

When is converting BMP to PNG a good idea?

Conversion makes sense when you need a smaller, lossless image that works reliably on websites and across common platforms. PNG is particularly suitable for screenshots, interface elements, diagrams, pixel art and images containing text.

• Website assets: convert a legacy BMP before adding it to WordPress, a documentation site or an HTML page.
• Software screenshots: use PNG to retain sharp text and hard edges without JPEG artefacts.
• Logos and diagrams: PNG compresses repeated colours and large plain areas efficiently.
• Sharing: PNG is easier to preview in browsers, messaging services and cloud storage interfaces.

For example, network-layout.bmp containing boxes, labels and connecting lines is a suitable candidate for network-layout.png. The PNG stores the same type of raster image but will commonly occupy less space.

Conversion is less useful when a photograph must be made as small as possible. BMP to JPG may produce a smaller file, although JPG uses lossy compression and can introduce artefacts. Converting a BMP that was originally made from a low-quality JPG into lossless PNG will not restore the detail already discarded by JPEG compression.

How large will the converted PNG be?

The PNG will usually be smaller than an uncompressed BMP, but there is no fixed reduction ratio. File size depends on the image dimensions, colour depth and how predictable the neighbouring pixels are.

A 1,920 × 1,080 24-bit BMP needs about 5.93 MiB for raw pixel data, plus its headers and any row padding. A PNG of a simple chart may be substantially smaller, while a photograph or noisy scan may still produce a fairly large PNG because its pixels are harder to compress. PNG may also be larger than a JPG of the same photograph because PNG does not discard image information.

Problem files and practical limits

BMP has several historical variants, including indexed-colour, bitfield and run-length encoded files. A malformed header, truncated data or an unusual encoding can stop software from decoding the image even when the filename ends in .bmp.

Very large bitmaps require enough device memory for the browser to hold decoded pixels and create the PNG. Decoding a large BMP and encoding the resulting PNG may therefore slow down or fail on a memory-constrained phone or tablet. Empty and corrupt BMP files cannot be decoded into valid PNG images.

Spaces, numbers, punctuation and accented or non-Latin characters in a filename do not alter the bitmap pixels. However, if another application refuses the generated PNG, save it with a shorter plain filename to avoid filename-length or character restrictions.

Frequently asked questions

Will the PNG keep the BMP file's original date?

Do not rely on the source BMP's filesystem date being retained by the downloaded PNG. A downloaded PNG is a newly created file and will normally receive a new creation or modification time from the browser and operating system. If the date forms part of an archive record, store it separately.

Why does my converted image still have a white background?

The white area is probably stored as ordinary white pixels in the BMP. PNG can represent transparency, but conversion cannot reliably decide which colour should be removed, particularly when the same colour appears elsewhere in the image. Use an image editor to select or mask the background.

Does converting to PNG improve print quality?

No. The conversion does not add pixels, sharpen blurred detail or increase the source resolution. Check the pixel dimensions against the intended print size before sending the PNG to a printer.

Why is a file rejected even though its name ends in .bmp?

The extension alone does not prove that the contents are a valid bitmap. The file may have been renamed from another format, damaged during transfer or written using a BMP variant that the decoder cannot read. Try opening it in its original application and exporting a fresh BMP or PNG.

Does conversion make an untrusted BMP safe?

Converting an untrusted BMP to PNG should not be treated as a malware scan. Keep the browser and operating system updated, and scan BMP files from unknown sources before asking the browser to decode them. After saving the PNG, open it in the application where it will be used and check that the image appears complete and correctly coloured.