How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

Started 2 months ago | Discussions thread
J A C S
J A C S Forum Pro • Posts: 15,480
Re: Correction

Currantos wrote:

There is perfectly clear notion what noise is.

There was at least one long thread in the PST forum about that and the bottom line was that it was not clear.

It is the erroneous signal present in the image that was not present in the original object introduced by the imaging device.

What is erroneous signal? To define that, you need to define signal (without errors) in the first place. Shot noise is a part of the signal. Is it noise then? Is an under or over exposed image noisy? Are geometric distortions noise? What is "the original object introduced by the imaging device"? The object is typically in front of that device.

It has two components, systematic and random.

This has been discovered at the time the normal distribution was discovered and statistics was born. All measurements were found to have "noise", ie. variations from ground truth state.

They were? All of them? Who did that?

If you would like to have better visualization of what noise is take a picture of pure uniform gray paper and look closely at it. The pixels that stand out, i.e. that are darker and brighter than the overall background. The darker/brighter pixels were not present in the original paper and are the 'noise' of the photographic system. (yes, there is 'noise' in the paper, it is not perfectly uniform, but that noise is an order of magnitude below the noise of the photo equipment and is therefore disregarded here).

Hope that helps.

There are other definitions of noise depending on different industries and fields, like acoustics, etc but all boil down to the same thing and are studied with same statistical formulas.

Which ones?

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