Luminance and noise with polarizer?

[andyptak]

Geez guys, 'nuff already. I didn't say that LR had only one Noise Reduction adjustment - chroma. What I said was that the default adjustment of LR affects chroma only. The default for the luminance slider is at zero - maybe indicating that Adobe agree with Seth (?) even though my own experience is to the contrary.

This started off as a simple question - did anyone know if a polarizer induced an increase in luminance noise by reducing the luminance of the sky?

[bjanes]

bjanes - I don't have to check my notes - I have ears, which is why I asked the question twice. Maybe Seth misunderstood the question (I doubt it) but I definately did not misunderstand the answer. While I and others may disagree with the answer, Seth is a very sharp guy and I don't dismiss what he says lightly. The fact that LR default NR is chroma only means that someone at Adobe agrees with Seth.

I am confident that luminance noise has nothing to do with the lens. Shot noise, the major component of noise in any image, is a property of light itself and is present even before the light enters the lens. If you want a scientific explanation of noise, see this post by a real scientist. Nowhere is the lens mentioned. The main contributors to digital image noise are shot noise, read noise, and pixel response nonuniformity. With long exposures dark current may contribute, but it is not a significant factor for most situations where exposure is considerably less than one second.

Roger Clark is another scientist who has analyzed noise. His method eliminated pixel nonuniformity, and shot noise and read noise account for the total measured noise without taking the lens into account. I would not place much confidence on hearsay evidence of an authority who was likely misquoted.

[andyptak]

I have heard of a technique - forget the proper name - used by night shooters, where they do a black frame also, in order to tame noise. I presume it's "sandwiched" with the real night shot and takes the randomness out of the noise. Never been able to find out how it's done though, so I don't know how appropriate it may be.

[bjanes]

I have heard of a technique - forget the proper name - used by night shooters, where they do a black frame also, in order to tame noise. I presume it's "sandwiched" with the real night shot and takes the randomness out of the noise. Never been able to find out how it's done though, so I don't know how appropriate it may be.

It's called dark frame subtraction. All you have to do is to take the image of the dark scene and then another with the same exposure time and then subtract it from the original image. It can be done automatically on most higher end cameras, but obviously doubles the time needed to capture the image.