Nikon D780 Reference Manual page 181

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NEF (RAW)
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NEF (RAW) image files (extension "*.nef") contain the raw data output
from the image sensor.
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Using Nikon's ViewNX-i or Capture NX-D software, you can adjust and
re-adjust settings such as exposure compensation and white balance as
often as you please without degrading image quality, making this
format ideal for photos that will be processed in multiple different ways.
ViewNX-i and Capture NX-D are available free-of-charge from the Nikon
Download Center.
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The process of converting NEF (RAW) images to other formats such as
JPEG is referred to as "NEF (RAW) processing". You can save NEF (RAW)
images in other formats using the ViewNX-i and Capture NX-D
computer applications or the [NEF (RAW) processing] option in the
camera retouch menu.
Shooting Settings
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