What exactly is the new Nikon sRAW file format?

Nikon-D4s-RAW-S-small-file-format

Image credit: WEX Photographic

The D4s was the first Nikon camera to support the new sRAW format (aka NEF RAW size S file format) and the rumored D800/D800E replacement is also expected to have it. In the latest [NR] blog's discussions there were some confusion on what exactly sRAW is. Here are some interesting findings on the new Nikon sRAW format from rawdigger.com (there is much more detailed technical information on their website):

  • It contains not RGB but YCbCr data much like a JPEG
  • The data is 11-bit
  • The tone curve is applied to the data
  • The in-camera white balance is applied to the data
  • The pixel count is 4 times less than with regular NEF files
  • The color information is shared between two adjacent pixels (in other words, chroma is recorded for each other pixel)
  • The file size is insignificantly smaller than full resolution 12-bit lossy compressed NEF
  • Compared to a regular NEFs the data needs additional processing (linearization) while converting it to a TIF/JPEG, that may cause additional problems during the conversion (see Study 3 below) as well as some additional computational errors
  • There is some loss of color accuracy in shadows, which negatively affects the usable dynamic range if color accuracy is important.
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