f-number equivalent between m43 and FF

Started Mar 25, 2014 | Discussions thread
Jack Hogan Veteran Member • Posts: 6,646
Defining Signal

olliess wrote:

mosswings wrote:

dwalby wrote:

OK, now I see your reasoning and I guess its a matter of how you want to define noise. I was defining it in terms of what is the probability that the sampled pixel accurately represents the expected signal value...

...

A curious exchange. Indeed bob is right in that "noise" is an emergent property of a signal stream, not a single measurement, so a time series for a single sensor or a spatial matrix for pixel array is required to observe it.

"Noise," as with "Signal," is what you define it to be. It's true that meaningful statistical properties of noise can only be estimated when there's more than one measurement, but that doesn't mean that a single measurement doesn't contain noise.

Light from an illuminant is reflected by the scene, travels through/is transformed by the lens and hits the sensing plane forming a 2D image.  In this context I believe that the signal is

1) the 2D image projected on the sensing plane - in photometric/radiometric units;
2) the 2D image in 1) filtered, sampled spatially, converted to e- through the photoelectric effect and integrated by the sensor during the time of exposure - in units of e- per pixel of a given channel.

Mean Signal in a specific area of the image is therefore the average of the photometric/radiometric quantity under the given image area or the average of the photoelectrons generated by a sensing element in a given channel in the same area of the image.

What do you think?

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