ELI5; What causes the “grain effect” in cameras and eyes when trying to look in very low light conditions?

Question

EDIT: So I get the camera part but what about the eyes?

In: Other

Answer 1

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.