ICO to NEF Converter

Encoding: the ICO uses each size stored as a headerless BMP or as a complete PNG; NEF uses uncompressed, lossless compressed, lossy compressed, or High Efficiency on recent Z bodies, 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; NEF allows 12 or 14 bits per channel, and the DNG written here has 8 bits per channel, linearised.

Colour: RGB or a palette, per image in the ICO; NEF supports camera RGB from a Bayer mosaic, 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; NEF can carry EXIF and Nikon maker notes, partly encrypted, plus a thumbnail and a larger preview, 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.

NEF is the raw format of Nikon cameras, from the D1 to the current Z series. It stores 12 or 14-bit sensor data, uncompressed or compressed, with a JPEG preview the camera renders using its Picture Control.

NEF is TIFF-based: the first directory usually holds a small thumbnail, and sub-directories hold the sensor data and, on current bodies, a full-size JPEG preview. Nikon's maker notes are a TIFF structure of their own, and since the D2X their white-balance block is encrypted with a key derived from the camera's serial number and shutter count.

NEF files come from Nikon DSLRs (D-series) and Z-series mirrorless cameras.

Forms and workflows that ask for NEF usually feed a raw editor, and each of those opens DNG as well, so the DNG can take the NEF's place. Keep the ICO if you only need to view or share the picture.

What NEF offers when it comes straight from the camera: Lossless compressed mode with no data loss; Picture Control recorded so Nikon NX Studio can reapply it; 12 or 14-bit sensor data. Its drawbacks: Partly encrypted maker notes; The lossy compressed mode discards some sensor data; Large files on high-resolution Z bodies.