ISO 800+ -- high noise

Started 2 months ago | Discussions thread
John Deerfield Veteran Member • Posts: 3,425
Re: ISO 800+ -- high noise

But if I understand what you're saying, with digital cameras, one increases ISO to increase amplification

of the signal (and light generates the signal)

in a low light situation,

In any situation really. Increasing the ISO is an amplification of the signal, regardless of the strength of the signal.

but low light has greater noise,

I wouldn't phrase it that way. Low light has less signal. In turn, the amplification of this signal has more noise.

so the increased amplification at higher ISO will in turn amplify the noise?

Any amplification will increase the noise regardless of ISO. It is going to boil down to a signal-to-noise ratio. Why can you use ISO 800 in bright light and not "see" the noise? Because in bright light there is more signal. When you use ISO 800 in low light, you have less signal (low light) and that means more noise.

To further complicate the matter, you can have multiple exposure values in any one given image. In other words, very bright areas of an image may look ok using a high ISO, but the shadow areas in the same image will look worse. Why? More signal in bright light, less signal in low light. The lower the signal, the more the noise, regardless of ISO. We tend to use higher and higher ISO's in lower light situations so we tend to associate a high ISO with more noise.

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