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by Aditya

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So my D90 offers "High-ISO Noise Reduction". Sounds like a good thing, but obviously there must be a cost of some kind. The settings are "Off", "Low", "Normal", and "High", and the default is "Normal".

What are the pros and cons of using this feature? Why not always set it to "High"? Or, should I be turning it off?

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I think your camera must do something like take a few photos then merge them together to reduce noise. So the cost would be time. –  tomm89 Oct 21 '10 at 4:40
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@tomm89, I don't think that's how it works –  seanmc Oct 22 '10 at 4:01
    
That's what commented instead of answering your post. –  tomm89 Oct 23 '10 at 0:08
    
In camera noise reduction (mainly long exposure NR) drains lots of battery... Consider that as well. –  user6944 Oct 17 '11 at 19:39
    
Why does long exposure NR take more battery? Isn't it running the same algorithm over the captured image no matter what shutter speed? –  Imre Oct 17 '11 at 20:18

3 Answers 3

up vote 6 down vote accepted

The pro's are self-evident:

  • Lower noise on high-iso

The biggest con:

  • Loss of detail

The high-iso noise reduction might remove detail mistakenly. While newer camera algorithms have gotten better at it, it's still not fool proof.

The settings between Off, Low, Normal and High dictate the amount of tolerance used for the setting, which affects the amount of detail that might be lost.

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4  
To add to this, if you have time and the software, you can get much superior results by doing noise reduction yourself on RAW files. Not only can you tweak settings, you can mask the NR layer differently on sections where you want to keep more detail. Here's an example of the amount of improvement you can get: pentaxforums.com/forums/1226753-post1.html –  Eruditass Oct 21 '10 at 5:37

In general I wouldn't recommend doing anything in camera that is irreversibly "baked" into the image, as such things can always be done better, with more control, and more importantly the option to undo, in post on your PC.

There is another feature called Long Exposure Noise reduction which shoots a black frame (i.e. one in which the shutter is closed) in order to remove "hot pixels" and other artefacts which show up on long exposures. This feature is useful and can't be replicated in post, unless you shoot your own black frames (with the lens cap on and viewfinder covered).

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Why does the viewfinder need to be covered? –  Winston Smith Oct 21 '10 at 7:34
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Believe it or not light can come in through the viewfinder, bounce round the pentaprism and land on the sensor! The amount of light involved is very small, in regular shooting you wouldn't see it, but if you are doing a long exposure with the lens cap on it can become a problem. Some cameras have a viewfinder shutter (or a bit of rubber attached to the strap) to help with this. –  Matt Grum Oct 21 '10 at 7:47
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You should cover the viewfinder during long exposures, regardless of enabling Long Exposure Noise Reduction. –  Alan Oct 21 '10 at 17:22
    
A very good point –  Matt Grum Oct 21 '10 at 17:41
    
so I guess that was one of my (unasked) questions: Does the feature affect the RAW image, or is it something that can be "undone" in post-processing? Your answer implies that the original is modified in camera. –  seanmc Oct 22 '10 at 4:03

Like many in-camera features, this boils down to how much do you trust your camera manufacturer vs. how much do you think you can do better yourself by doing it manually in post-production.

As others have noted, once you do something in-camera, you often can't undo it in post. With noise reduction, you'll be losing image detail just like you would when applying noise reduction via Lightroom, Noise Ninja, or other software. The difference is that when you do it yourself, you have more control.

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