Electronic Format RAW Image File
The RAW file format used by Nikon which has the extension .nef is similar to a digital negative and contains all the the data and information captured when the photograph was taken.
NEF images usually have 12 or 14 bit data when compared to 8 bit JPEG files.
NEF files can be opened by many Graphics programs usually through the use of plug-ins, they can then be processed by the user.
» Nikon ViewNX
How to open .nef files?
Software to open .nef files
What are .nef files