Confused about ISO

[DeeCajun]

Could someone please ( ever so simply..) explain what causes some photos to be grainy at ISO 200 and others grain free at ISO 2500 ? :scratch

[adbsgicom]

Underexposure would be my guess assuming you are talking about the same camera (or class of camera). The noise is mostly in the darker area, so if you underexpose and have to bump it up by 2 stops, you bump up all the noise.

[DeeCajun]

I guess this is something that just doesn't sink in ... thank you for trying to help me.

I like to shoot at dusk, so I bump up the ISO, even at 200 i see grain

today i saw a photo, shot at dusk with a ISO of 2500 that was clear

What am I missing?

[Qarik]

forget about iso. You will get noise if you underexpose a shot.

[DeeCajun]

how can I forget about it? Aren't I supposed to bump it up when I need more exposure?

[Qarik]

how can I forget about it? Aren't I supposed to bump it up when I need more exposure?

you can underexpose a shot at iso 200 or iso 2500. Thus you can get noise at 200 or 2500. You can underexpose and get noise at any ISO. The noise is potentially worse at higher iso's because higher iso can have noise even when properly exposed.

[Nikonic1]

There are three things that contribute to your final exposure (and noise content). Shutter, Aperture, and ISO. Any of these being off, creating an off exposure, will result in (some) noise.

[Pupator]

I guess this is something that just doesn't sink in ... thank you for trying to help me.

I like to shoot at dusk, so I bump up the ISO, even at 200 i see grain

today i saw a photo, shot at dusk with a ISO of 2500 that was clear

What am I missing?

As the others have said, underexposing images is the fastest route to noise. However, also keep in mind that the ISO 2500 photo you saw may have been put through a noise removal program like neat image or noise ninja.

[DeeCajun]

I want to get this, I have been trying all winter, maybe too hard, I'm a smart gal, but it's not clicking..

Thanks for all of your help I am surely going to try to put it to good use.

[ziggy53]

If you are using the Canon XT/350D and you underexpose, that will definitely cause some noise to appear in shadow regions during recovery. If you boost the contrast, that adds to the problem.

A more currently produced FF camera, properly exposed, can be nearly noise free at higher ISOs.

Do you have some examples of the problem you are experiencing? Ideally images straight out of the camera and with full EXIF. If you post original JPGs in an unprotected SmugMug gallery so that we can download the original image, that would be great in letting us see the problem.

[DeeCajun]

If you are using the Canon XT/350D and you underexpose, that will definitely cause some noise to appear in shadow regions during recovery. If you boost the contrast, that adds to the problem.

A more currently produced FF camera, properly exposed, can be nearly noise free at higher ISOs.

Do you have some examples of the problem you are experiencing? Ideally images straight out of the camera and with full EXIF. If you post original JPGs in an unprotected SmugMug gallery so that we can download the original image, that would be great in letting us see the problem.


Yes yes, a new camera, it's on the list...

I will search for the picture I took that was at ISO 200 with noise, it was in the house which has horrible lighting, I guess I was under the wrong impression that the ISO would boost the exposure in the photo.. and now even more confused on why/when you bump it...

In a magazine I was reading there was a photo I loved, taken at dusk with an ISO 2500... but as it was mentioned, noise could have been removed and there was better exposure somehow..

I just know one day all of this will make sense.. but right now, not so much!

[ziggy53]

Some links that elaborate on why proper exposure and the "expose to the right" method are so important.

http://www.luminous-landscape.com/tutorials/expose-right.shtml

http://www.outdoorphotographer.com/how-to/photoshop-and-other-software/the-myth-of-protective-underexposure.html

[zoomer]

You see the noise when you take an underexposed (dark) photo and bump up the exposure (brighten it) in processing...all of a sudden there is all this noise that appears. The higher the ISO the worse it will be.

If you take a photo at high iso 2500 and you take it as bright as possible without blowing it out there will be less visible noise.

Yes the ISO contributes to noise but the actual exposure can make just as much difference when you need to increase the brightness of a photo in processing.

Same thing everybody else is saying just worded it a bit differently.

[pathfinder]

There are two kinds of noise, and I am not referring to luminance or color noise. I am talking about on the monitor versus in the print, on paper. Which are you talking about? Much noise seen on a monitor, ceases to be an issue in a print on the wall.

[DeeCajun]

first thank you so so much for helping this confused girl...

The noise i am referring to appears on the monitor, like zoomer said, when you bump up the exposure, and brighten it..

Thanks ziggy I am clicking the links now.. :bow

[VayCayMom]

I guess this is something that just doesn't sink in ... thank you for trying to help me.

I like to shoot at dusk, so I bump up the ISO, even at 200 i see grain

today i saw a photo, shot at dusk with a ISO of 2500 that was clear

What am I missing?


ISO 200 is not "high" that is what I use outdoors as a standard, I never go lower.

[DeeCajun]

ISO 200 is not "high" that is what I use outdoors as a standard, I never go lower.


Thank you.. Now the reason for bumping it up outdoors is to boost the sensor's sensitivity to light?

My partner is taking me out to dinner.. I requested to go at dusk as there is a lake along the way.. *snicker*

i will try to boost that ISO and not get noise! ( although I am fairly certain I dont know how other than long exposure time)

[TonyCooper]

I want to get this, I have been trying all winter, maybe too hard, I'm a smart gal, but it's not clicking..

Thanks for all of your help I am surely going to try to put it to good use.

The only way to really find out is to get out there at dusk and shoot the same shot with different exposure, speed, and iso settings. Compare them and see which combination results in noise and which doesn't.

It's much easier to understand something in practice - looking at multiple shots of the same thing - than it is in theory.

[topcat374]

Think you might find this link to a previous thread (http://www.dgrin.com/showthread.php?t=158761)helpful:) The book referred to ('Understanding Exposure) really helps to clarify things too. HTH.

[DeeCajun]

The only way to really find out is to get out there at dusk and shoot the same shot with different exposure, speed, and iso settings. Compare them and see which combination results in noise and which doesn't.

It's much easier to understand something in practice - looking at multiple shots of the same thing - than it is in theory.


This is exactly what I did, and it worked! I changed settings and looked over things in PP, I had very little noise even at higher ISO :thumb

Slowly but surely...

Topcat thank you, i am checking out the link you posted now..

Thanks so much everyone, not getting this stuff is way out of my comfort zone, I really am a smart cookie. I love learning though!

[The_Fat_Zebra]

After all this good advice, one more thought: if I'm not shooting manual (most of the time), I'll put my camera at +0.3EV extra as a standard. For noise, better to have room to move down in exposure than to move up.

[bmoreshooter]

The best way to understand this is : take ISO out of the equation for just a moment. A photo exibits its best qualities when all things are done correctly. A properly exposed photo in perfect light gives the best final results. If you under expose the picture you will have to correct it in PP. This is where the grain is introduced. The worse the exposure the more grain you will see. Photo scenes that have deeper shadow areas and are darker overall require more coorection to bring up to normal so increased grain is a result.
Now to put the ISO back in. We increase the ISO when we can't get enough light from the scene to achieve a proper exposure without changeing anything else. It allows us to shoot at faster shutter speeds or lower f-stops. Increased ISO = more grain. This situation has been improved with the current upgrades in cameras. So, a picture shot on ISO of 2000 on an older camera is not going to be as good as ISO2000 on a more current camera.
Finally, don't raise the ISO unless it is necessary to get the shot. Remember that there is always a sacrifice for our actions. Try to consider adding more light or a tripod.

[Scott_Quier]

So many explainations getting so close to the crux of the matter.

The noise in an image file is, in part, a function of ISO. But, one can get a clean image at any ISO, be it 100 or 3200 (well, there are some older cameras that pretty much stop at 800 :D). The trick is to expose correctly and not attempt to correct under-exposure in post.

There is noise in every image. In a correctly exposed image, this noise is such a small percentage of the data in the image file that it gets swamped by that image data and becomes very much less visible. Noise becomes appearant when one attempts to boost exposure in post.

Now, under-expose an image. For any given ISO, the noise data level is still the same, but the image data is very much less, thereby making the noise data a much larger percentage of the data in the file. When you boost the exposure in post, you apply that amplification to both the noise and the image data to the same degree. Now the noise is very much more appearant.

So, you want less noise in you images? Expose your images to maximize the amount of image data (see the "Expose to the Right" pages referenced above) to increase your signal-to-noise (S/N) ratio. Then correct (reduce) the exposure in post to make it look right.

There are trade-offs in every photographic decision (TANSTAAFL) - exposing to the right requires either a slower shutter speed, larger aperture, or faster ISO.

A classic example - shooting sports, where the quantity of light is at premium, one needs a faster shutter speed to stop the action. But that means that one would need to open the lens a bit. But, one needs to have a good DOF because the chances of getting enough of the player in focus when they are moving with a shallow DOF are vanishingly small. So, that means one needs to use a smaller aperture. That leaves either under-exposing the shot or boosting the ISO to get the aperture and shutter speed required to get the desired result. I believe (and there may be exceptions to this - the chances an absolute statement being 100% correct are quite small) it's always better to boost the ISO in camera than it is to boost exposure in post.

[topcat374]

So many explainations getting so close to the crux of the matter.

The noise in an image file is, in part, a function of ISO. But, one can get a clean image at any ISO, be it 100 or 3200 (well, there are some older cameras that pretty much stop at 800 :D). The trick is to expose correctly and not attempt to correct under-exposure in post.

There is noise in every image. In a correctly exposed image, this noise is such a small percentage of the data in the image file that it gets swamped by that image data and becomes very much less visible. Noise becomes appearant when one attempts to boost exposure in post.

Now, under-expose an image. For any given ISO, the noise data level is still the same, but the image data is very much less, thereby making the noise data a much larger percentage of the data in the file. When you boost the exposure in post, you apply that amplification to both the noise and the image data to the same degree. Now the noise is very much more appearant.

So, you want less noise in you images? Expose your images to maximize the amount of image data (see the "Expose to the Right" pages referenced above) to increase your signal-to-noise (S/N) ratio. Then correct (reduce) the exposure in post to make it look right.

There are trade-offs in every photographic decision (TANSTAAFL) - exposing to the right requires either a slower shutter speed, larger aperture, or faster ISO.

A classic example - shooting sports, where the quantity of light is at premium, one needs a faster shutter speed to stop the action. But that means that one would need to open the lens a bit. But, one needs to have a good DOF because the chances of getting enough of the player in focus when they are moving with a shallow DOF are vanishingly small. So, that means one needs to use a smaller aperture. That leaves either under-exposing the shot or boosting the ISO to get the aperture and shutter speed required to get the desired result. I believe (and there may be exceptions to this - the chances an absolute statement being 100% correct are quite small) it's always better to boost the ISO in camera than it is to boost exposure in post.

Really useful explanation Scott - and makes perfect sense:) I think I've just decided to do a little investigating in the field!