What causes "Noise?"

[NateNLogansDad]

So I'm heading to The World on Friday......wait for applause..... and I realized that this is the first trip my Nikon D5100 will be going to Florida. Every other trip, I've had the D5000 which did fairly well with handling noise at 3200 but I tried to keep it at 1600 or below because noise DRIVES ME NUTS!

I do remember some pictures that were taken in a darker room having more noise than other pictures taken in a decently lit church...both with the ISO set to 3200.

So, my question is this.....

Not including the capabilities of the camera, what causes noise? Is it darker pixles, light reflecting off of your subject, what? Can you see a scene and know it's going to be noisier than another at the same ISO?

I took the D5100 out front the other night with poor lighting and took a few pictures of my jeep at ISO 6400 and was shocked the the noise was less noticeable than the D5000 at 3200 and I'm scared to push it up that high on darker rides next week if the noise will be more noticable. (hence the noise software reduction post I started already.)

Am I the only one who freaks out about how my pictures are going to turn out right before a trip??? This is supposed to be a vacation for goodnes sakes!

 

[VVFF]

Everything electrical has a certain amount of noise. A sensor is particularly sensitive to noise because it has gain.

Think of it like the antenna you may have for TV in your house. Your antenna receives a very small signal. Out of that small signal it needs to create something more "significant" that can be read by the TV and turned into a picture that uses 300W to be displayed!

To do this it has to be amplified.

When you increase the ISO, you are effectively increasing the amplification of the sensors sensitivity to light. In the process you also amplify the noise that is inherent in the sensor itself. Some of this comes from light scatter and such but most of it is just part of the fact that everything electronic produces some amount of noise. It's similar to how your engine in your car can never be perfectly balanced and will always produce some vibration...or how it can never be 100% efficient.

In terms of your question about well lit scenes showing less noise. This is also inherent of electronics. In electrical terms its called signal to noise ratio. For the circuit, there is a noise floor. It might be useful to talk about this in sound recording terms since it is easier to visualize. When you record sound on your computer(or cassette tape! haha) you'll notice some hiss in the background. You may even be able to hear this on some CDs depending on the sound quality of the CD. This hiss is the "noise floor". It should only be really obvious when the recorded audio is quiet. Once the volume picks up, the hiss is drowned out.

The same is true for light reaching our sensor. The sensor has a certain amount of inherent noise at the particular ISO setting. If the signal(light) that reaches the sensor can raise this above the noise floor(near black) then a significant portion of the noise will be "masked" and no longer visible.

This is why ISO isn't always the desired solution to obtaining low light images. While it can do it...noise is VERY visible in night scenes and, unless movement is in the scene that isn't desired, it usually is better to use a stable surface and a low ISO setting.

Hope this helps!

 

[NateNLogansDad]

I had to read that nice and slow, but in the end my eye's lit up like when my 5 yr old sounds out a hard word for the first time Thank you very much, that was very well written

In essence, even at ISO 100 in complete darkness, there is some noise but since it's not amplified it really isn't noticable?

 

[boBQuincy]

Not including the capabilities of the camera, what causes noise? Is it darker pixles, light reflecting off of your subject, what? Can you see a scene and know it's going to be noisier than another at the same ISO?

What causes noise? Physics. All electrical devices have noise when an electrical signal passes through them. Most of it is usually thermal, one reason astro sensors are cooled to a really low temperature. Our visible noise is analogous to hiss in an audio system and can't be eliminated but can be minimizd and to some extent removed after the fact by processing.

The noise is a form of (unwanted) signal and is easier to see in dark areas (no or low signal) since the ratio of signal to noise is low. Any scene where the camera boosts exposure of dark areas is likely to show more noise than other areas of the image.
Avoiding underexposure helps to minimize noise but when there just isn't enough light we don't have many options.

 

[VVFF]

I had to read that nice and slow, but in the end my eye's lit up like when my 5 yr old sounds out a hard word for the first time Thank you very much, that was very well written

In essence, even at ISO 100 in complete darkness, there is some noise but since it's not amplified it really isn't noticable?

Correct, at ISO 100 the noise floor is lower because the noise+signal is not amplified as much making the noise much less noticeable and less light required to "cover up" any noise that is present (signal to noise ratio is higher because the noise floor is lower than at higher ISOs).

 

[photo_chick]

The ISO numbers are based on light sensitivity and approximate the standards set forth in film. They are supposed to be standard across all cameras, but sensors are not. So ISO 100 not necessarily the point at which you see the least amount of noise. On some cameras it's 100, some it's 200, some it's 50... It's not usually enough of a change to tell a difference in standard prints but you can sometimes tell a difference if you get into pushing exposures and things like that. But noise does become amplified when you go down as well as up.

 

[Gianna'sPapa]

Am I the only one who freaks out about how my pictures are going to turn out right before a trip??? This is supposed to be a vacation for goodnes sakes!

No your not alone! In 40 days, I'm heading down with a new camera body (K5) and a couple new lenses. I probably could leave one of our K10's home, but because I'm not yet comfortable with the K5, I bringing my old reliable K10. I will probably not use it, but its like Linus' blanket, its got to be there.

 

[LPZ_Stitch!]

The noise is a form of (unwanted) signal and is easier to see in dark areas (no or low signal) since the ratio of signal to noise is low. Any scene where the camera boosts exposure of dark areas is likely to show more noise than other areas of the image.

This is why following the methodology of ETTR (Expose To The Right) generally brings lower noise pictures, even when you're using higher ISOs.

By keeping your histogram as far to the right as possible, without blowing highlight, and bringing it back down to "normal" in PP, you'll get smoother, less-noisy pics.

 

[photo_chick]

This is why following the methodology of ETTR (Expose To The Right) generally brings lower noise pictures, even when you're using higher ISOs.

By keeping your histogram as far to the right as possible, without blowing highlight, and bringing it back down to "normal" in PP, you'll get smoother, less-noisy pics.

While it's better to overexpose than underexpose, it it's properly exposed you'll usually just catch the right side of the histogram anyway. Anything more will be blown out and loose details. And there are sacrifices when you bring down the exposure in post. There's always a tradeoff for everything.

 

[LPZ_Stitch!]

While it's better to overexpose than underexpose, it it's properly exposed you'll usually just catch the right side of the histogram anyway. Anything more will be blown out and loose details. And there are sacrifices when you bring down the exposure in post. There's always a tradeoff for everything.

Right ... the point of ETTR is to expose as far to the right *without* blowing highlights as possible.

Over on the Canon Photography-on-the-Net site, it's pretty much been conclusively proven that with Canon cameras, ETTR returns the highest signal-to-noise ratios even when using higher ISOs.

Here's a good thread discussing the technical reasons and showing examples: Are you Shooting HAMSTTR? - ETTR - Expose to the right

This may not be the case with all brands of cameras, but it's certainly true for Canons.

 

[zackiedawg]

I find the best method isn't necessarily exposing to the right, but nailing the exposure. Noise is part of the signal noise from boosting the sensitivity, however, noise lives primarily in underexposure - boosted shadows. Highlights show very little noise, and properly exposed midtones. So the better you expose the shot, the less the noise, even at higher ISOs. While I agree with the basic theory that an ISO100 shot will have less noise than an ISO1600 shot because of the lower sensitivity and signal noise, I generally find that there are limitations to how much a strongly underexposed low ISO shot can be boosted in post processing to match a proper exposure made at ISO1600 - other issues begin to surface besides just noise - color fidelity, dynamic range, etc. So in the end, I still find properly exposing the shot by using the right ISO to usually be the better option (for me) than underexposing or overexposing and trying to fix later. And many times, I've seen an ISO1600 shot that showed significantly less noise, better color, and better detail than a poorly exposed ISO400 shot that had to be adjusted in post processing to a proper exposure. If I'm shooting ISO1600 and notice I can't quite get the shutter speed I need, I can either shoot a stop under and adjust in post, or bump ISO to 3200 and properly expose and compose the shot in camera, I'll go for ISO3200 every time. Some of this could come down to preferences - some folks love tons of processing - adjusting RAW exposures, pulling up shadows, running noise reduction, etc...I'm so much happier when I get a clean, low noise, good color, properly exposed shot out of the camera. And most modern cameras (like your D5100) can easily shoot to ISO3200 and deliver straight-from-the-camera JPG results that can be printed large - ISO1600 can be noise-free right out of the camera. It's all dependent on nailing the exposure.