Siehe auch "Nikon NEF File Format":...
NEF file layout
NEF files are often referred as a proprietary format, but this is not completely true: indeed they are
compliant with the TIFF 6.0 specifications. Basically TIFF files are composed by a set of Image File
Directories (IFD), which are small data blocks describing the contents of the file (not only graphics
information such as resolution, size and so on but even photographic information such as shutter
speed, aperture, comments, copyright notices and so on). They usually contain a single image, but
they can hold more than one (most of times the secondary images are thumbnails, reduced-size
copies of the main image which can be previewed quickly). Manufacturers can add proprietary tags,
which Nikon did, so the proprietary part in NEF files is actually a small part.
Indeed the most important information is about the way pixels are coded. They can be coded in
many ways, and TIFF supports the notion of Color Filter Array (CFA), that is the way most digital
sensors capture data: r-g-b components are not recorder for each pixel, but only one primary at a
time (not necessarily r-g-b). The image has to be interpolated to be viewed.
...
http://www.tidalwave.it/projects/nefio/NEF.pdf