Why do cameras capture noise even when it's pitch black?
Even if you hide the camera in a black bag at night time, it still captures noise?
Obviously it can't be light photons since there are none..So what it is?
Even if you hide the camera in a black bag at night time, it still captures noise?
Obviously it can't be light photons since there are none..So what it is?
Copyright © 2024 QUIZLS.COM - All rights reserved.
Answers & Comments
Verified answer
They don't "capture" noise -- they *produce* noise.
And other artifacts that aren't "noise."
Your camera's sensor has a "bias" current that helps "hold" the charge photons produce when they hit the sensor. This bias current is subtracted out after amplification when the analog to digital conversion occurs, but because the bias current isn't exactly the same in every pixel, when it's amplified it will produce varying pixel values that average out to the bias value, but vary from pixel to pixel. That's noise. The amplifiers themselves also add a bit of noise, since they're not all identical.
Finally, there's a bit of "dark current" -- electron flow in the pixels that occurs even if they're not hit by light, and varies by temperature. That's not actually "noise" though, since it's not random; the same pixel at the same temperature turned on for the same amount of time (your exposure time) will produce almost exactly the same dark current every time. Dark current is an artifact (stuff in the pixels that's not "signal"), but since it's not random it's not "noise." The longer you have the sensor turned on, the more the dark current builds up. But being non-random, it can be removed pretty reliably -- that's what the "long exposure noise reduction" function on your camera does. It takes a second "exposure" without any light hitting the sensor so you only get an "image" of the dark current (called a "dark frame"), and then it subtracts that from the regular exposure to remove the dark current. It's poorly named, since it's dark frame subtraction and not noise reduction...
The higher the ISO you set, the more the pixel current is amplified -- and the "noise" in the pixels gets amplified right along with the signal. So the higher the ISO, the more noise is visible in the image.
Peace.
It is random electrical impulses caused by the sensor heating up, trying to capture something.
Try an experiment. Instead of having you camera on some automatic setting, use Manual and set a 1/250 exposure when you take that shot in the dark. I'll net you have almost no noise.
The answer you received already is correct, where digital photography is concerned. There is a similar effect in film photography because the film itself has texture -- which in printing can come across as noise.