In Camera Noise Reduction

Can anyone explain the noise reduction process for a Nikon DSLR. I certainly understand that one can chose the level of noise reduction but I am wondering how the electronics of the camera determines when to use it. Or, is there a specific level of noise reduction applied to all jpegs regardless of whether is needs it or not, based on what one has selected? If the camera applies noise reduction, does it increase the sharpening to compensate for any noise reduction applied?

There are two types of noise reduction in a Nikon (and most other cameras) - High ISO and Long Exposure - all done in processing. High ISO noise reduction looks for hot and dark pixels, and blends them with surrounding pixels, with a loss of resolution and visible artifacts. Long exposure, in my D3, takes a dark frame, shutter closed, after the shot for the same exposure time. Hot pixels are detected in both frames and cancelled in processing. AFIK, it works for RAW too.

 

I generally leave both off, because I'd rather see noise than worm tracks.

I generally leave both off, because

 

In my vast or half-vast experience, I find that noise reduction in post processing gives me more control than what the camera does on it's own.

As Do I, since I shoot entirely RAW, it really makes no difference if its on or off, though. I am trying to understand how the camera reacts to noise in a jpeg. What I have noticed during some very (unsophisticated) tests is that jpegs straight from the camera, with a normal amount of noise reduction applied, appear to be somewhat cleaner and sharper than images in RAW, and processed in Lightroom.

I thought the great benefits of Dark Frame Subtraction (Long. Exp. NR) cannot be reproduced in any other way?

I thought the great benefits of Dark Frame Subtraction (Long. Exp. NR) cannot be reproduced in any other way?

 

Than what? I have a lens cap and the ability to do some dark frame subtraction in post that suggest it doesn't have to be automated (though I might not turn down a feature to do this in camera automatically but still deliver the raws).

I thought the theory was that a subsequent (almost simultaneous) Dark Frame removes the noise created by things like thermal effects and such.

 

Doing it two days later is missing the random stuff.....

I thought the theory was that a subsequent (almost simultaneous) Dark Frame removes the noise created by things like thermal effects and such.

 

Doing it two days later is missing the random stuff.....

 

Oh, I meant taking the capture at the time (if not entirely, if you need a lens cap), just doing the subtraction later.