ICO to DNG Converter

Encoding: the ICO uses each size stored as a headerless BMP or as a complete PNG; 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 to 32 bits per pixel, set per size in the ICO; DNG allows 8 to 16 bits per channel, and the DNG written here has 8 bits per channel, linearised.

Colour: RGB or a palette, per image in the ICO; 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 ICO stores it as 8-bit alpha in 32-bit and PNG entries, or a 1-bit mask in old icons; the DNG has none, so transparent areas are filled with the colour you choose.

Other images: the ICO can hold several sizes of the same picture, typically 16, 32, 48 and 256 px; only the main image is converted.

Metadata: the ICO can carry only a directory of the sizes inside, with no EXIF; DNG can carry EXIF, XMP and DNG tags for colour matrices, calibration and lens corrections, but nothing is copied across.

ICO is a container that bundles several sizes of the same icon (16, 32, 48, 256 px) into one file. It is still the most compatible format for website favicons and Windows app icons.

An ICO starts with a 6-byte ICONDIR (type 1 for icons) and a 16-byte entry per image giving width, height, colour count and offset. Each image is either a BMP without its file header plus an AND mask, or a complete PNG.

ICO files usually come from website favicons, Windows programs and installers.

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 ICO suits favicons and Windows icons.

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.