EDIT: So I get the camera part but what about the eyes?
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In cameras it is a noise. When taking a photo in low light you have to open a shutter for longer time so that each cell of the sensor can “capture” enough light. Because the sensor is not perfect it generates some noise. So the longer shutter you have the more of both signal and noise you get.
Similarly in audio when you have weak signal and amplify it you amplify the noise as well.
I guess you “see noise” in your eyes as well. I. Not sure though.
The sensor in the camera can be more or less sensitive to light. What we are worried about referred to SNR (signal to noise ratio), the more sensitive the sensor the more of that SNR is actually noise and that noise shows up as a grain. When you have a lot of light available you turn the ISO (image sensor sensitivity) WAY down so the it only picks up obvious signal and not much noise. You have little to no grain and the image looks almost perfect.
So… Nobody knows about the eye explanation ?
I dunno but I get irl grain sometimes so possibly the camera is gaining sentience?
Further research is needed!
Let’s say that a color for each of the camera’s pixels can have a value between 0 (very dark) and 1000 (very bright). Under low light conditions all those subpixels would have very low values (let’s say between 0 and 5) so you amplify (i.e. multiply) them to get the full range of brightness you’d expect. Otherwise the image would be mostly dark. The issue here is that the smallest amount of noise or deviation can have a large impact. For example if you read 2 instead of 3, then multiply it with 200 you’ll get a huge error. Gradients will also look bad because you only have a few steps.
These small errors are called noise and can happen because of heat or interference.
In video it’s from high ISO, which is needed in low light situations. It’s similar to cranking up the volume of a microphone if the source is too far away. Eventually you’ll pickup the source you want, but now you’re also amplifying all of the other ‘noise’ around it.
In video, when you crank up your sensor sensitivity (high ISO) you do the same thing. The sensor is now picking up al of the ‘noise’, but it’s represented as a grainy effect.
There is no grain effect in eyes. There is a black and white effect though, where in extreme low light, objects lose colour because different cells are fired in the eyes.
Astronomers know this, when looking into an telescope eyepiece at a nebula one is advised to look at it with averted vision after having charged up the cells by not looking at any light sources (except dim red light)
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