PNG to BMP Converter

PNG is compressed and supports transparency; BMP is the plain Windows bitmap that older software, game engines and modding tools, embedded screens and some printers require. This converter decodes each PNG in your browser and writes either a 24-bit BMP, with transparent areas filled with a colour you pick, or a 32-bit BMP that keeps the alpha channel. "PNG to bitmap" means exactly this conversion.

How to use this tool

1. Drop one or more PNG files.
2. Choose 24-bit (most compatible), 32-bit to keep transparency, or 8-bit greyscale.
3. For 24/8-bit pick the background colour for transparent areas; optionally set a DPI or a max size.
4. Download the BMPs.

Formula

24-bit: 54 bytes of headers + height × (width × 3 rounded up to a multiple of 4). 32-bit: a 108-byte BITMAPV4HEADER (122 bytes of headers) + height × width × 4, with bit masks R 00FF0000, G 0000FF00, B 000000FF and A FF000000.

Transparent pixels are composited on the background: out = colour × α + background × (1 − α). In 32-bit files the alpha is stored unpremultiplied, like PNG. Paint, Photoshop, GIMP and current browsers read 32-bit BMP alpha; some older programs ignore it and show the hidden colours, so use 24-bit there.

Example

A 160 × 100 PNG becomes a 24-bit BMP of 54 + 100 × 480 = 48,054 bytes or a 32-bit BMP of 122 + 100 × 640 = 64,122 bytes. A half-transparent red pixel (255, 0, 0, α = 128) on white becomes (255, 127, 127) in the 24-bit file and stays (255, 0, 0, 128) in the 32-bit file.