D90 Does Noise
Reduction on NEFs at Longer Exposures
Prepared 2008-11-01 (150/223874) by Bill Claff
I analyzed pairs of "lens cap" shots taken with no
noise reduction turned on in the camera at a variety of exposures (ISO 200).
I had previously analyzed data for the D200, D300, and D3.
And like the D200, D300, and D3; the analysis proves that the D90 performs
noise reduction at longer exposures.
First, here is a chart of noise versus exposure time (in stops).
(There is an extra data point at 1/800s and one missing at 8s)
Note the drop in noise at exposures of 1s or longer.
To confirm that this is a result of noise reduction I performed 2D Fast Fourier
Transforms (2D FFTs) on the center 256x256 portion of the images.
Here are the results for 9 different exposures:
(I used an aggressive Levels adjustment to make the patterns more obvious.)
The exposure times were:
1/15 |
1/8 |
1/4 |
1/2 |
1 |
2 |
4 |
15 |
30 |
Note the white centers starting to form at exposures of 1s and longer.
This is proof of (inter pixel) noise reduction.