D800 and D4 Pattern Noise Analysis with FFTs

Certain types of pattern noise and signal processing can be detected using 2D FFTs (Fast Fourier Transforms).

I performed such an analysis of dark frames (raw) from a D800 and a D4 using ImageJ.
Here's the D800

And the D4

The ISOs from left to right are ISO 50, ISO 1600, ISO 6400, ISO 25600, and ISO 102400 (D4).
The images have been darkened to accentuate the patterns.

Sometimes I find it helpful to view the images from several feet to see subtle features.
The "ideal" FFT would be a uniform gray.
A good guide to interpreting FFTs is here:
http://qsimaging.com/ccd_noise_interpret_ffts.html

Strong vertical or horizontal lines general indicate pattern noise in the horizontal or vertical direction respectively. Both cameras exhibit some pattern noise.

Little "ticks" along an axis is usually a sign of banding, often due to unbalanced channels in a multi-channel readout scheme. This seems very well controlled in both cameras.

The classic "spherical" look of signal processing is absent. There is no evidence of additional signal processing being applied to the raw. In Nikon cameras that general takes place at longer exposures such as 1/4s and longer and will be the subject of a separate study.
--
Bill (visit me at http://home.comcast.net/~NikonD70/ )