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When I take low-light photos with my Sony NEX-5R, I find that I stick to ISO 200 to ensure acceptable noise.

I was told that fear of ISO will hold me back, and that I should do noise-reduction in software. I always thought of noise-reduction as reducing detail (there's no free lunch), but maybe I'm wrong, so I wanted to check: how much does noise-reduction let me increase ISO without a noticeable loss of quality -- either an increase in noise, or a reduction in detail, or some other aspect? If I shoot at ISO 200 without doing NR in post, can I shoot at ISO 400 if I'm doing NR in post? 800? 1600? 6400? I expect to not notice a difference if I switch back and forth between the two photos.

I have Lightroom 5, and Nik Dfine, but not Topaz DeNoise (though I'm willing to try it out and buy it if it makes a huge -- rather than incremental -- difference). I don't have Photoshop. I'm also willing to use other software, provided it's not command-line, runs on the Mac, and is cheap (like $20, not like $100).

Is there a rule of thumb (like: "NR lets you increase ISO 8x"), or is the answer just to try it out?

I don't print my photos, and I don't view them at 100%, either, but full-screen on my monitors.

Here's an example of the kind of photo for which I noticed the noise:

enter image description here

At ISO 400 or above, the sky (not visible in this crop) is no longer black but grayish / noisy.

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    From my limited experience with NR in post, it also depends on the scene in the picture. Some scenes/motives are better/worse for extreme NR. – Håkon K. Olafsen Jan 9 '14 at 8:04
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    Because your camera is a Sony I bet you'll want to read the answer to this question about noise reduction in-camera vs software. – Esa Paulasto Jan 9 '14 at 9:11
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    I think you should just try it out, as image quality and loss of quality are subjective. – Saaru Lindestøkke Jan 9 '14 at 9:26
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    Fear of ISO IS holding you back!!! :-). See DXO optics camera sensor ratings with a low light emphasis. Their rating for the NEX5r is ISO 810. They say" Low-Light ISO indicates the highest ISO sensitivity to which your camera can be set while maintaining a high quality, low-noise image (based on a Signal-to-Noise-Ratio [SNR] of 30dB, a dynamic range of 9EVs and a color depth of 18bits)." - if you need 4 x the light above the level at which DxO adjudge the quality "high quality low noise" then you may need to buy a Nikon Df :-) – Russell McMahon Jan 9 '14 at 10:05
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    Please put in a photo which actually demonstrates the issue you're talking about, not one where you've cropped it out - that no help to anybody. – Philip Kendall Jan 9 '14 at 14:09
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You are correct that there is no free lunch. Software NR works by looking for sharp edges and trying to identify what is detail and what is noise, but at a very fine level, they can't be distinguished. What you will normally see with light NR is a reduction in fine detail, but gross detail is maintained. The more you turn up NR, the more gross the detail loss will become, but also the more noise will be reduced. In this way, NR is really very similar to a more selective form of resolution reduction. It preserves the strong, high contrast transitions, but you still lose the fine, subtle detail.

You will always lose some detail, particularly noticeable when looking very closely at the image. The trick is to balance the loss of detail and the removal of noise. How well it works is going to depend a great deal on the scene and what point is an acceptable trade off is going to depend a great deal on the viewer.

That said, ISO 200 is extremely low and you should be able to use a much higher ISO without significant noise issues. As mentioned by Russell McMahon in the comments, your camera should be able to go to at least ISO 800 without any major issues.

  • Here's an example photo: i.stack.imgur.com/MYEoe.jpg for which I was comparing. I find that at ISO 400 and above, the sky (cropped out in this photo) is no longer black but grayish / noisy. – Vaddadi Kartick Jan 9 '14 at 14:04
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    @KartickVaddadi - well, yes, the sky would be greyish because it is actually getting exposed. You can drop down the black point and deal with both the noise and the non-black sky while still gaining the advantages of better low light performance. – AJ Henderson Jan 9 '14 at 14:30
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You're correct, a higher ISO will introduce noise and cause detail to be lost. However, it's important to understand how far you can increase ISO before it makes a noticeable impact. By the numbers, I'm sure that increasing one stop from 100 to 200 will undoubtedly result in a nearly imperceptible difference under pretty much any condition. I bet going from 200 to 400 is also a very small difference, though perhaps more easily recognized.

There are a few other considerations, however (that you've answered). If you're making large poster-sized prints, a high ISO (and the resulting noise and loss of detail) could be real trouble and cause you to have a terrible-looking wall-sized print. On the other hand if you are only posting a small image to the web, the image will be resized to something so small that noise will disappear and fine detail won't matter. That is, ISO 200 may be required for one use, while ISO 12,800 is perfectly acceptable for another.

Additionally, consider your subject and how it will handle the noise/detail change. A subject with lots of fine detail will benefit more from a lower ISO than something where detail is less important or obvious. Shadows will typically show off noise more than highlights, too.

Of course, for the kind of image you've posted, carrying a tripod and shooting at the base ISO is going to yield the best results.

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Your intuition is right. As you raise noise-reduction, details get lost too. This means that there is no way to make photos more usable with noise-reduction alone.

What most people do though is apply noise-reduction, particularly for color-noise which is often a separate control in software and then downscale. The result is a lower-resolution image which looks better than had you simply reduced its size.

This happens because the reduction in size hides image softness better than it does uneven colors and noise.

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Noise reduction does not let you raise ISO without loss of quality. I find that slight chromatic noise reduction is good when you shot in low light (regardless of ISO setting) and generally I find a noisy image preferable to a luminance NR'ered image because the image has more details under those grains and the neighboring pixels look more natural. It is more interesting for me to tweak the curves and use the grains to my advantage as I develop the image in lightroom that to make it look fake through NR.

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