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Higher ISO or underexpose then corrected in PP?

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mosum

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If a scene calls for a higher ISO for a correct exposure, for a given shutter speed and aperture would you underexpose the scene with a lower ISO (thus less noise and "perceived" higher DR) and then lift up the exposure in PP, or use a higher ISO to begin with?

Here I'm talking about underexposing by no more than 1 stop, and images acquired in RAW.

Thanks for your insights.
 
mosum said:
If a scene calls for a higher ISO for a correct exposure, for a given shutter speed and aperture would you underexpose the scene with a lower ISO (thus less noise and "perceived" higher DR) and then lift up the exposure in PP, or use a higher ISO to begin with?

Here I'm talking about underexposing by no more than 1 stop, and images acquired in RAW.
Click to expand...
It depends; what camera, and what ISO range?

--
emil
--



http://theory.uchicago.edu/~ejm/pix/20d/
 
This is a great question I was wondering the same thing. Say with a d800 and 6400 ISP or choose 1600 ISO then fix in pp
 
mosum said:
If a scene calls for a higher ISO for a correct exposure, for a given shutter speed and aperture would you underexpose the scene with a lower ISO (thus less noise and "perceived" higher DR) and then lift up the exposure in PP, or use a higher ISO to begin with?

Here I'm talking about underexposing by no more than 1 stop, and images acquired in RAW.

Thanks for your insights.
Click to expand...
It largely depends upon whether underexposing will cause the lose of shadow detail. It detail is lost, no amount of PP will fix that. The old film adage was expose for the shadows and develop for the highlights. Some of that still applies to the digital world.
 
JosephD05 said:
This is a great question I was wondering the same thing. Say with a d800 and 6400 ISP or choose 1600 ISO then fix in pp
Click to expand...
If your raw converter does an accurate job of exposure compensation, then 1600 pushed two stops in the raw converter will be as good as 6400, except that you will have two more stops of highlight headroom. There are very few cameras that benefit from an ISO more than 1600, such that a higher ISO slightly reduces the apparent noise. More typically, beyond this point, it's the low exposure that results in the noisy appearance, not the amount of ISO gain being applied.

--
emil
--



http://theory.uchicago.edu/~ejm/pix/20d/
 
mosum said:
If a scene calls for a higher ISO for a correct exposure, for a given shutter speed and aperture would you underexpose the scene with a lower ISO (thus less noise and "perceived" higher DR) and then lift up the exposure in PP, or use a higher ISO to begin with?
Click to expand...
Everything I know on this subject I learned from ejmartin, so he is the authority. FWIW, this is where I think exposure strategy is at circa 2012:
http://forums.dpreview.com/forums/read.asp?forum=1018&message=38342664

As far as the D800 is concerned, looking at DxOmark's and bclaff's graphs, one favors 1600, the other 6400, but the difference is so slight that it may be immaterial.

Cheers,
Jack
 
If this is about the D800 I can venture a guess based on my expectations. My D700 gives me about 2 stops of headroom for recovering detail in highlights. I expose to the right of the histogram (within limits) without worrying too much over a few blown highlight "blinkies". I can recover the detail in post.

I doubt that the D800 will be as forgiving and will probably be more prone to blown highlights. However, if the D800 sensor is, as they say, comparable to the performance of the D7000 then you will pick up a few stops of detail in the shadows without pulling up excessive noise. Something my D700 won't do as well. Nikon has finally wrestled their chronic amp noise problem to the ground. I would tend to be more careful exposing the highlights with the D800 though and a little less concerned over slightly underexposed images.

It sounds like you take two different routes to the same end point.
 
mosum said:
If a scene calls for a higher ISO for a correct exposure, for a given shutter speed and aperture would you underexpose the scene with a lower ISO (thus less noise and "perceived" higher DR) and then lift up the exposure in PP, or use a higher ISO to begin with?
Click to expand...
You will never get less noise by underexposing. You will get at least as much noise, probably more.

It's not turning up the ISO setting on the camera that causes the noise, it's the low light that is the cause.

Whatever you do, underexposure is a sure way to increase noise.
 
I mostly agree with kenwj.

Also don't foget that this is a 'digital camera' so every thing gets digitised to 14 bits. So when you look at the histergram and you have flat lines at the ends, low or high, then you are throughing away that part of your DR. Good exposure is the key. Higher ISO does add noise but it also spreads the available light over your full digitisation range (14bits) .

I hope this is helpfull.
 
ejmartin said:
mosum said:
If a scene calls for a higher ISO for a correct exposure, for a given shutter speed and aperture would you underexpose the scene with a lower ISO (thus less noise and "perceived" higher DR) and then lift up the exposure in PP, or use a higher ISO to begin with?

Here I'm talking about underexposing by no more than 1 stop, and images acquired in RAW.
Click to expand...
It depends; what camera, and what ISO range?
Click to expand...
The more complete answer: Go to DxOmark.com, look up the measured dynamic range for your camera. At some point the DR drops by one stop for every one stop increase in ISO. At this point, increasing the ISO doesn't do much for you; the one stop decrease in DR comes entirely from the loss of one stop of highlight headroom due to the increased amplification of a one stop higher ISO, not at the expense of lost shadow capability. Below this point, where the DR curve flattens, the flattening is coming from a poorer shadow performance due to noise in the camera electronics (read noise); boosting the exposure in the raw converter will bring up that extra shadow noise together with the image, and you will do better to use a higher ISO in the camera. BTW, note that the ISO indicated by the camera is what DxO calls 'manufacturer ISO' when you click on a data point of the DR graph.

There is one caveat -- DxO does not measure pattern noise; if your camera has pattern noise issues when you try to bring up the exposure in a raw converter, you should check whether the pattern noise is made less apparent by using a higher ISO for the same exposure (shutter speed & aperture).
--
emil
--



http://theory.uchicago.edu/~ejm/pix/20d/
 
In general, use the higher ISO. High ISO is done by increasing the gain of the analog amplifiers, which never increases their S/N ratio and should decrease it at least a bit. Also, analog noise (increased amplifier gain) is easier to deal with in PP than quantization noise (posterizing) caused by small digital signal range.
 
I've had profound success using higher ISO and overexposing (exposing to the right) than using suggested ISO with suggested exposure or lower ISO and relying on PP.
 
After doing numerous tests shooting sports in a dimly lit gym, I had the most success with nailing the exposure, and then doing a bit of NR in PP, rather than under exposing. This is with either my d300 or d800. Nailing wb is crucial as well since any pping will amplify noise.
 
Just took a couple of test shots with a D700 converting the files with NX2. 100% crops with no NR enabled in the camera or added in post. Neutral Picture Control. No sharpening applied. Noise levels and detail look the same.

f1/.8, 1/160 ISO 3200



f/1.8, 1/160, ISO 1600 +1 stop in RAW

 
mosum said:
If a scene calls for a higher ISO for a correct exposure, for a given shutter speed and aperture would you underexpose the scene with a lower ISO (thus less noise and "perceived" higher DR) and then lift up the exposure in PP, or use a higher ISO to begin with?
Click to expand...
Quite a while ago I seem to remember Julia Borg (wife of Ilia Borg?) doing just such an experiment. Her conclusion was that it was better to underexpose and lift the exposure in PP than it was to use a higher ISO.

But as I said, that was a long time ago, with cameras several generations older than what we have now. This wouldn't be a difficult experiment to conduct yourself.
 
mlitscher said:
Quite a while ago I seem to remember Julia Borg (wife of Ilia Borg?) doing just such an experiment. Her conclusion was that it was better to underexpose and lift the exposure in PP than it was to use a higher ISO.

But as I said, that was a long time ago, with cameras several generations older than what we have now. This wouldn't be a difficult experiment to conduct yourself.
Click to expand...
With the example I posted, ISO 1600 pushed a stop looks slightly better than ISO 3200 if I stare at them for a while but in print I'd never be able to tell them apart.
 
ejmartin said:
JosephD05 said:
This is a great question I was wondering the same thing. Say with a d800 and 6400 ISP or choose 1600 ISO then fix in pp
Click to expand...
If your raw converter does an accurate job of exposure compensation, then 1600 pushed two stops in the raw converter will be as good as 6400, except that you will have two more stops of highlight headroom. There are very few cameras that benefit from an ISO more than 1600, such that a higher ISO slightly reduces the apparent noise. More typically, beyond this point, it's the low exposure that results in the noisy appearance, not the amount of ISO gain being applied.
Click to expand...
I've been puzzled by some of the findings on the D800 in regards to this. Looking at Bill's DR Shadow Improvement chart, it shows the D800 improving in shadow response up to ISO6400.

But then it's also been suggested that the analog gain leaves off around ISO1000. Surely digital multiplication alone would not produce an increase in shadow DR in the range above ISO1000. Yet I've never heard of noise reduction being suggested as a factor until after ISO6400. I've heard the suggestion of "gain sharing" but not seen that idea advanced conclusively. Still puzzled over how this one actually works.

In a practical way, I'm pursuing that Brooklyn Bridge shot I showed you earlier. Minus the iPad billboard. Should I use ISO1600 and underexpose? According to Bill's Shadow Improvement chart, I should go straight to ISO6400. [A time exposure would not work well in this situation; the Brooklyn-Queens Expwy runs under the promenade and it shakes a lot.]

I wonder if these newer sensors have gone one step beyond ISOless to a hybrid approach? Yes the sensor captures 14-stops a priori. The electronics can actually read it, so one might think the entire thing should be ISO-less. And yet it seems as though the engineers are still wringing out optimizations in the use of pre-conversion gain staging and circuit topology.
 
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