Files with the .NEF extension contain uncompressed digital images saved in raw form, namely just as they were captured by the digital camera CCD sensor, using a 12-bit or 14-bit format. The information contained in NEF files concern also the image metadata, such as the camera manufacturer and model name, as well as focal length and other photographic parameters. The format is unique to Nikon cameras. To be able to read these files, the used photo editing software must support them.

Raw NEF files allow for non-lossy, repeated editing – the information about exposure, hue, sharpness, and white balance are saved separately, as instructions that generate a resulting file, still using the same raw NEF materials as the base.