BMP to PNG Converter

Encoding: the BMP uses usually none; RLE for some 4 and 8-bit files; PNG uses lossless DEFLATE with a prediction filter chosen per row, and the download is a lossless 8-bit PNG with full alpha.

Bit depth: 1, 4, 8, 16, 24 or 32 bits per pixel in the BMP; PNG allows 1, 2, 4, 8 or 16 bits per channel, and the PNG written here has 8 bits per channel.

Colour: RGB or an indexed palette in the BMP; PNG supports RGB, greyscale, or an indexed palette of up to 256 colours, written here as 8-bit sRGB.

Transparency: the BMP stores it as an optional fourth byte in 32-bit files, which many programs ignore; the PNG keeps it as a full alpha channel, so edges and shadows can fade smoothly.

Metadata: the BMP can carry nothing beyond the header's resolution fields (and a colour profile in rare V5 headers); PNG can carry text chunks, an ICC profile, physical resolution and EXIF in an eXIf chunk, but nothing is copied across.

BMP stores raw, uncompressed pixels. Files are huge but trivially simple, which is why some legacy Windows software, embedded displays and printers still ask for it.

A BMP is a 14-byte file header ('BM' and the offset to the pixels), a DIB header (40 bytes, or 108 and 124 bytes in the V4 and V5 versions that add colour masks and alpha), an optional palette, then pixel rows padded to 4 bytes and normally stored bottom-up.

BMP files usually come from Windows Paint, legacy Windows programs, embedded displays and some scanners.

PNG stores pixels losslessly with full alpha transparency. It is ideal for screenshots, logos, UI and anything with sharp edges, but photos saved as PNG are several times larger than JPEG.

A PNG opens with an 8-byte signature and is a chain of chunks, each with its own CRC: IHDR (size, depth, colour type), optional PLTE and tRNS for palettes, one or more IDAT chunks with the compressed rows, and IEND.

PNG is the better choice for screenshots, logos, graphics and anything that needs transparency, while BMP suits legacy software and embedded systems that require it.

PNG strengths: Lossless: no quality loss, ever; Full transparency with smooth edges; Perfect for text, screenshots and graphics. Drawbacks to weigh: Large files for photographs; No standard animation (that is APNG).