High ISO noise question.
Apr 16, 2016 08:10:30 #
Psergel wrote:
I used the example of a brick wall to try to keep ... (show quote)
Your gray card idea is good. What you say is sound. I'm hoping Alan Myers might join this discussion and get into the technical aspects of the subject.
Apr 16, 2016 08:39:00 #
Simple response: The stronger signal from a well-lit image overcomes the image noise.
You have seen the difference in signal-to-noise ratio in the images. This concept confuses, in part because it describes a characteristic of electronic circuity that always generates noise (useless information) which goes with the non-noise (useful information) portion of the image.
Here the term "signal" means that portion of the image that makes up the useful information of the image.
The term "noise" refers to the useless information in the image.
So if the image contains way more signal in relation to noise, then the image will obviously appear nearly noise free.
I will stop here knowing that probably most readers still will not grasp this controlling behavior of the electronic circuits in the camera's processing activity. In fact, noise arises from other sources as well.
You can read more here:
https://en.wikipedia.org/wiki/Signal-to-noise_ratio
You have seen the difference in signal-to-noise ratio in the images. This concept confuses, in part because it describes a characteristic of electronic circuity that always generates noise (useless information) which goes with the non-noise (useful information) portion of the image.
Here the term "signal" means that portion of the image that makes up the useful information of the image.
The term "noise" refers to the useless information in the image.
So if the image contains way more signal in relation to noise, then the image will obviously appear nearly noise free.
I will stop here knowing that probably most readers still will not grasp this controlling behavior of the electronic circuits in the camera's processing activity. In fact, noise arises from other sources as well.
You can read more here:
https://en.wikipedia.org/wiki/Signal-to-noise_ratio
abc1234 wrote:
Funny you should ask because I am currently testin... (show quote)
Apr 16, 2016 09:16:44 #
The noise appears more in the dark areas / underexposed shots due to the increase in the noise to info ratio. There is more data gathered at the light end of the histogram, and therefor the same amount of noise appears less due to the denominator effect. The ratio of noise/info is less. I believe the amount of noise is the same, but in the dark areas, there is less info so the ratio is higher and it appears more. This is the justification for ETTR shooters. Sorry for the non-technical explanation, but I believe right.
Cheers,
Cheers,
abc1234 wrote:
Funny you should ask because I am currently testin... (show quote)
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Apr 16, 2016 10:18:50 #
Psergel wrote:
I used the example of a brick wall to try to keep ... (show quote)
Yes, the lower ambient light shot will have more noise even at the same ISO since it is a longer exposure. Long exposure = heat build-up = more noise. Why do you think digital cameras limit the length of exposure you can set? It's because the sensor and heat sinking around it is heating up and a hot sensor is noisier. If the lower light level were adjusted for by only a larger aperture, but the same exposure time, than I think the noise would be the same - but possibly the image quality would be poorer due to the larger aperture.
Apr 16, 2016 10:21:55 #
The answer to your question is more about sensor technology than camera or available light.
The newer cameras (i.e. Sony A7Rm2) shows little or no noise at ISO 6400 in the conditions you describe. What noise exists is easily removed in post. More MP helps, but the backlit FF sensor is a big reason.
The newer cameras (i.e. Sony A7Rm2) shows little or no noise at ISO 6400 in the conditions you describe. What noise exists is easily removed in post. More MP helps, but the backlit FF sensor is a big reason.
Apr 16, 2016 10:48:13 #
Psergel wrote:
Using a high ISO.....say 6400 taking two shots wit... (show quote)
The noise would be the same. It would be less noticeable in the first photo.
--Bob
Apr 16, 2016 11:00:00 #
There is virtually no "heat build-up" due to longer exposures.
What there is is twice the noise collected if the exposure is twice as long. This will only be generally visible for exposures in excess of 1 second.
It is also true that at higher ambient temperatures there is more noise.
Another factor in this case is higher "Photon Noise" at lower light levels.
And because the overall light level is lower for one shot the SNR will be lower and more read noise will be visible.
For those reasons two images using the same ISO will have different visible noise levels.
What there is is twice the noise collected if the exposure is twice as long. This will only be generally visible for exposures in excess of 1 second.
It is also true that at higher ambient temperatures there is more noise.
Another factor in this case is higher "Photon Noise" at lower light levels.
And because the overall light level is lower for one shot the SNR will be lower and more read noise will be visible.
For those reasons two images using the same ISO will have different visible noise levels.
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Apr 16, 2016 11:47:07 #
Apr 16, 2016 12:09:03 #
Rongnongno wrote:
Go back to your beloved krill.
Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans.
Eaten by many fish and mammals including some whales.
Or....as urban slang
Krill
Usually a person who
a)Smokes a BUNCH of weed
b)Wears V-Neck's
c)Constantly at little corner cafe's
In any case....I don't get it.
Apr 16, 2016 12:18:44 #
Apr 16, 2016 12:35:01 #
zigipha
Loc: north nj
1. so the iso is the same for both shots
2. and both shots are "properly exposed"
3. so in both shots the photosite wells will fill up to the same level
3.1 this happens before the readout, so there is no difference in readout noise
3.2 both shots will come out with the same dynamic range
So there are 5 or 6 sources of noise. The only one that is proportional to time is random noise; I would expect the longer exposure image to have more noice, but whether its visible depends on how much longer. If its 1/250 vs 1/30, i doubt you would see a difference; if its 1/250 vs 30 seconds (with aperature and ND filter), I think you would see a differences.
Also the longer time exposure image is subject to more motion blur; watch out for that.
2. and both shots are "properly exposed"
3. so in both shots the photosite wells will fill up to the same level
3.1 this happens before the readout, so there is no difference in readout noise
3.2 both shots will come out with the same dynamic range
So there are 5 or 6 sources of noise. The only one that is proportional to time is random noise; I would expect the longer exposure image to have more noice, but whether its visible depends on how much longer. If its 1/250 vs 1/30, i doubt you would see a difference; if its 1/250 vs 30 seconds (with aperature and ND filter), I think you would see a differences.
Also the longer time exposure image is subject to more motion blur; watch out for that.
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Apr 16, 2016 12:36:20 #
Psergel wrote:
Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans.
Eaten by many fish and mammals including some whales.
Or....as urban slang
Krill
Usually a person who
a)Smokes a BUNCH of weed
b)Wears V-Neck's
c)Constantly at little corner cafe's
In any case....I don't get it.
Eaten by many fish and mammals including some whales.
Or....as urban slang
Krill
Usually a person who
a)Smokes a BUNCH of weed
b)Wears V-Neck's
c)Constantly at little corner cafe's
In any case....I don't get it.
It's another case of two Hogs that, either mutual or unilateral, have this "thing" that anything proposed by one cannot be allowed to just lie there, but must be poked and proded for no reason apparent to any onlookers.
Apr 16, 2016 13:09:01 #
zigipha wrote:
1. so the iso is the same for both shots br 2. and... (show quote)
Thank you.
This makes sense and is pretty much what I thought.
The only reason I asked is because I think I see more noise in longer exposure images. Not real long....more like your 1/30 example.
Apr 16, 2016 13:09:48 #
Apr 16, 2016 13:16:47 #
Some will argue even that ISO does not properly belong in the Exposure Triangle as a variable of exposure for digital cameras.
neilds37 wrote:
It's another case of two Hogs that, either mutual or unilateral, have this "thing" that anything proposed by one cannot be allowed to just lie there, but must be poked and proded for no reason apparent to any onlookers.
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