this post was submitted on 17 Nov 2023
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Photography

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Where does noise really come from? (alien.top)
submitted 11 months ago by VexTheMaster@alien.top to c/photography@viewfinder.pro
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I know, I know, it can be caused by various factors, like high ISO, poor lighting conditions, long exposure time, heat. (not that I know why the last two cause noise)

But where does noise REALLY come from? What is noise? What does it have to do with photons and photosites?

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[โ€“] eddiewachowski@alien.top 1 points 11 months ago (1 children)

This was a rabbit hole I went down recently that was quite illuminating.

Sensors have a native ISO and any extended (higher or lower) are simply the sensor amplifying or decreasing the signal.

[โ€“] oldlurker114@alien.top 1 points 11 months ago

Sensors have a native ISO

No they do not. ISO is an output format (e.g. JPG) metric defined by ISO 12232 standard. It has nothing to do with image sensors.

Most cameras do change the operational parameters of the image sensor when the ISO setting is changed, typically the PGA (programmable gain amplifier) setting is changed and the signal is amplified the more the higher the camera's ISO setting is.

and any extended (higher or lower) are simply the sensor amplifying or decreasing the signal.

That is not right.

Typically the ISO 100 (sometimes something else) setting on a camera is such that the image sensor is run at the lowest PGA amplification setting. Anything above that and the amplification is increased (and/or digital multiplication is used in software). The "extended lo" settings typically operate the sensor at the very same setting the ISO 100 does, just change the metering and processing of the data.