BMP to DNG Converter

Encoding: the BMP uses usually none; RLE for some 4 and 8-bit files; DNG uses lossless (or lossy) JPEG-compressed sensor data, plus optional JPEG previews, and the download is a Linear DNG: demosaiced 8-bit RGB with the colour matrices raw editors need.

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

Colour: RGB or an indexed palette in the BMP; DNG supports camera RGB plus the colour matrices that map it to XYZ (demosaiced linear RGB in a Linear DNG), 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 DNG has none, so transparent areas are filled with the colour you choose.

Metadata: the BMP can carry nothing beyond the header's resolution fields (and a colour profile in rare V5 headers); DNG can carry EXIF, XMP and DNG tags for colour matrices, calibration and lens corrections, 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.

DNG is Adobe's openly documented raw format. Some cameras and phones record it directly, Adobe DNG Converter turns other brands' raw files into it, and a Linear DNG holds already-demosaiced RGB that raw editors treat like any other raw file.

DNG is built on TIFF/EP. The raw image sits in a sub-IFD marked as the main image, with tags for black and white levels, colour matrices and the colour filter pattern; a Linear DNG (PhotometricInterpretation 34892) stores demosaiced RGB instead of a mosaic. Previews are optional, and Adobe DNG Converter can write a medium (1024 px), full-size or no preview.

DNG is the better choice for raw editing and archiving raw files in an open format, while BMP suits legacy software and embedded systems that require it.

DNG strengths: Open specification read by every raw editor; Lossless compression and optional previews; Recorded directly by Leica, Pentax, DJI drones and phones. Drawbacks to weigh: Large files; No browser or ordinary photo viewer support on every platform.