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Convert BMP to PNG

Files never leave your device. All processing happens in your browser.

Pixels. Leave empty to keep the original dimensions.

How to convert BMP to PNG

  1. 1

    Add your BMP files.

  2. 2

    Conversion runs immediately and keeps every pixel value exactly.

  3. 3

    Download PNGs that are far smaller but identical in content.

This is the rare conversion with no downside. BMP and PNG are both lossless, so every pixel value survives untouched — but PNG actually compresses, while BMP essentially does not. You get the same image, bit for bit, in a fraction of the space and a format that everything can open.

Identical pixels, much smaller file

PNG uses DEFLATE compression combined with per-row filters that predict each pixel from its neighbours. Applied to a bitmap this is highly effective, because BMP stores raw data with no compression to get in the way. Typical reductions run from 50% on noisy photographic scans to well over 95% on screenshots, diagrams and anything with flat colour areas. The decoded image is mathematically identical either way.

When this is the right conversion rather than BMP to JPG

  • Scanned documents and text. PNG keeps letter edges perfectly crisp; JPEG softens them and small print is the first casualty.
  • Screenshots, UI captures and anything containing rendered text or thin lines.
  • Scientific, medical or measurement imagery, where the actual pixel values carry meaning and must not be altered.
  • Diagrams, logos, line art and CAD exports — flat colour is where PNG compresses best and JPEG looks worst.
  • Anything you intend to edit repeatedly, since PNG can be re-saved indefinitely without degrading.

The case for JPEG instead is essentially just photographs where you want the smallest possible file and can accept some loss.

Transparency and colour depth

BMP has a 32-bit variant with an alpha channel, though it is rarely used and support for it is patchy. Where it is present and your browser decodes it, the transparency carries into the PNG intact. Older BMPs using indexed palettes — 8-bit, 4-bit or monochrome — are expanded to full colour during decoding, which is why a small palette-based BMP can occasionally produce a PNG that is not as small as you expected.

Very large bitmaps

A high-resolution scan can easily be 100 MB or more as a BMP, and the whole thing has to be decoded into memory before the PNG can be written. On a phone that can exceed what the browser has available and the conversion will stop with a memory message. That is a device limit rather than a problem with your file — the same conversion usually succeeds on a desktop.

The conversion runs in this tab, on your machine. Nothing is uploaded, which matters when the bitmap came off a scanner and contains a document you would not want on someone else’s server.

Questions about BMP to PNG

Is any quality lost converting BMP to PNG?

None at all. Both formats are lossless, so the PNG contains exactly the same pixel values as the BMP. The only thing that changes is how efficiently those values are stored.

How much smaller will the PNG be?

Between roughly half and a twentieth of the original, depending on content. Screenshots, diagrams and text scans compress enormously; noisy photographic scans compress least.

Should I convert to PNG or JPG?

PNG whenever the exact pixels matter — text, screenshots, line art, scientific images, or anything you will edit again. JPG only when it is a photograph and you want the smallest possible file and accept some quality loss.

Does the transparency in a 32-bit BMP carry over?

Where the browser decodes it, yes — PNG stores a full alpha channel. Note that 32-bit BMP with alpha is uncommon and inconsistently written, so many files that look like they should have transparency do not actually contain it.

Why is my small palette-based BMP not much smaller as a PNG?

Indexed BMPs using 256 colours or fewer are expanded to full colour when decoded, so the PNG is written as a truecolour image rather than a palette one. The result is still lossless, just not as compact as a palette-preserving conversion would be.

The conversion failed on a huge scan. What happened?

Uncompressed bitmaps must be fully decoded into memory before the PNG is written, and a very large scan can exceed what a browser tab has available, particularly on a phone. Try on a desktop, or reduce the dimensions first.

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