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Exposure is key (plus a55 noise boasting ^^)

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AlexK-12

AlexK-12

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First off, I'd like to make a few assertions. I am by no means a professional (obviously) but I have been shooting for a few years. Second, this is by no means a scientific or well thought out visualization of how exposure affects the noise of an image. Last, I love my a55 and it does wonders for me!

I had read a couple of times that the way you expose your image can greatly affect noise performance. Some people never shoot above ISO 1600 yet some claim to achieve great quality pictures worthy of prints at ISO 3200 and even 6400. For the most part I believed them since I've seen some of the great shots at 6400. I wanted to push this a little farther and see how well a camera could handle at ISO 12800!

I shot a simple scene in very low light with the same aperture and ISO all hand held and then touched them up in lightroom with the same exact settings except with different adjusted exposure values. The following settings were uniform among the three images. (Again, not scientific).



Contrast: -15; Highlights: -15; Shdows: +15; Whites: +33; Blacks: -33; Clarity: -25

Sharpening: 25; Radius: 1.0; Detail: 25; Masking: 0

Luminance: 50; Detail: 50; Contrast: 0

Color: 25; Detail: 50







Here are the crops of each picture:




+1.3 EV picture






0.0 EV picture






-1.0 EV picture






As you can see, overexposing by a bit can greatly affect the noise of an image (even a poor one such as this) and even allow it to be usable for prints (okay, maybe at ISO 6400).

The sony a55 may not be the best high ISO camera, though I'm content with it, but with the proper exposure and post processing, it can produce some really decent pictures! Thank you for reading and any comments are always welcome (you know, because it's a forum).

--
-AlexK
 

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I like my a55..but with nr at auto or shooting raw. For me its great till 400 with j-pegs but i am a bit critical. If you are overexposing for lower noise though isnt that kind of pointless?

If i shoot at 800 because i need a bit more speed for birding say, wouldnt i get a clean image anyway possibly under-expossing(just a touch) at 200iso? mtfnr..now that can do wonders though


crop from pic below



 
Very true good sir. It has been a known for ages that more light = less noise. Just make sure not to confuse this with the pseudoscience that has been floating around here. Not sure what threads you were referring to, but the ones who claim raising iso results in less noise are confused. Raising iso isn't really capturing more light, it is a digital enhancement. You on the other hand are lengthening your shutter speed, resulting in more actual light, which makes sense it would reduce noise. Larger apertures or slower shutters work, increasing digital gain does not.
 
See, I'm still learning bit by bit about the science behind the image. What you are saying makes sense but I'm now just trying to figure out why. I've noticed that at ISO 100 and 1/4000 shutter speed can result in some noticeable noise (not much) which, if I am understanding you correctly, is because of the shutter speed? I just find it neat how clean this 12800 image is which is good to know, though I will probably never shoot anything higher than 3200 most of the time.
 
AlexK-12 said:
AlexK-12 wrote:

See, I'm still learning bit by bit about the science behind the image. What you are saying makes sense but I'm now just trying to figure out why. I've noticed that at ISO 100 and 1/4000 shutter speed can result in some noticeable noise (not much) which, if I am understanding you correctly, is because of the shutter speed?
Click to expand...
As you say yourself, exposure is key. An underexposed shot at ISO 100 will show more noise than a correctly exposed shot at ISO 100, but most likely only in shadows or darker parts. A severely underexposed shot at ISO 100 will show even more noise, also in lighter parts. When correcting an underexposed shot in post, you apply digital gain in post which brings up noise.

Underexposure hurts at any given ISO. It just hursts a lot more when shooting at higher ISO, as the digital gain applied in camera has allowed to use less light for a start. Hence the signal-to-noise ratio is already compromised.

If the ISO 100 shot you mention was underexposed only you know - unless you share it with us here.
 
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AlexK-12 said:
AlexK-12 wrote:

See, I'm still learning bit by bit about the science behind the image. What you are saying makes sense but I'm now just trying to figure out why. I've noticed that at ISO 100 and 1/4000 shutter speed can result in some noticeable noise (not much) which, if I am understanding you correctly, is because of the shutter speed? I just find it neat how clean this 12800 image is which is good to know, though I will probably never shoot anything higher than 3200 most of the time.
Click to expand...
 
Ah okay, this makes plenty of sense! So that's why full frames usually have better noise performance because they have larger photosites and thus collect light better. I've often heard about the signal to noise ratio. I might have to read more about it sometime. Thanks for the helpful comments :)
 
Filterless Sensor said:
Filterless Sensor wrote:

Very true good sir. It has been a known for ages that more light = less noise. Just make sure not to confuse this with the pseudoscience that has been floating around here. Not sure what threads you were referring to, but the ones who claim raising iso results in less noise are confused. Raising iso isn't really capturing more light, it is a digital enhancement.
Click to expand...
Way too simplistic and partially wrong. Raising ISO often also means an analogue boost of the signal, rather than digital. Which depending on the camera and ISO's, may also result in more or less read noise. Every camera has its own read noise curve and at a given physical exposure (shutterspeed, F stop and constant light source), a remaining factor is the above mentioned read noise. For example, a Sony A580 has it's lowest read noise around ISO 800, in which case you can end up with less noise at a given physical exposure, shooting at ISO 800 than using ISO 200 (or 3200...), even in RAW, if you're going to equal visible exposures after the fact. What you will lose though is some DR, but that's another discussion and may or may not be objectional for the given shot.

And then there's the factor of different in camera jpeg engines. The argument before wasn't that shooting at a higher ISO will show less noise with equal physical exposures, the argument was that it can result in more noise (read noise for example) or less detail due to extra NR in shadow areas (underexposed shot) vs less in brighter areas (brighter exposed shot at higher ISO, same physical exposure).

A simple example, full scene:

282a0ce48d6d4eca8380bdd397671647.jpg

100% crop ISO 1600 darker exposed (note physical exposures are identical):

ee8e3f3af24244f9a3829b7240c71c96.jpg

Same crop at ISO 3200:

48630bac5d014e359e8d54e877ecfe6b.jpg

And the former one brigthened to show there really is less detail (and less colour information) in the ISO 1600 shot due to NR:

ba5f6cf44fe649ada50e3410dc10827c.jpg
 
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TrojMacReady said:
TrojMacReady wrote:
TrojMacReady said:
Filterless Sensor wrote:

Very true good sir. It has been a known for ages that more light = less noise. Just make sure not to confuse this with the pseudoscience that has been floating around here. Not sure what threads you were referring to, but the ones who claim raising iso results in less noise are confused. Raising iso isn't really capturing more light, it is a digital enhancement.
Click to expand...
Way too simplistic and partially wrong. Raising ISO often also means an analogue boost of the signal, rather than digital. Which depending on the camera and ISO's, may also result in more or less read noise. Every camera has its own read noise curve and at a given physical exposure (shutterspeed, F stop and constant light source), a remaining factor is the above mentioned read noise. For example, a Sony A580 has it's lowest read noise around ISO 800, in which case you can end up with less noise at a given physical exposure, shooting at ISO 800 than using ISO 200 (or 3200...), even in RAW, if you're going to equal visible exposures after the fact. What you will lose though is some DR, but that's another discussion and may or may not be objectional for the given shot.

And then there's the factor of different in camera jpeg engines. The argument before wasn't that shooting at a higher ISO will show less noise with equal physical exposures, the argument was that it can result in more less noise (due to read noise for example) or less detail at the lower ISO due to extra NR in shadow areas (underexposed shot) vs less more detail in brighter areas (brighter exposed shot at higher ISO, same physical exposure).
Click to expand...
 
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