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Whenever I view my 12MP photos on my computer at 100% zoom (they're roughly 4200x2400), there always seems to be a lot of grain and noise to the image quality. What, specifically, causes this and what can be done to fix it?

Equipment:

  • Nikon D90
  • 18-105mm Nikkor AF-S VR Lens (stock)

I'd prefer not to use any software like Photoshop to remove it (because it's more of a workaround than an actual fix, and Photoshop isn't really in my workflow).

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7 Answers 7

up vote 16 down vote accepted

What you are seeing is an image noise -- random fluctuations that affect sensor pixels and cause them to measure value a bit above or bit below light that actually comes to the sensor.

The main factor that increases noise is how much is the signal from sensor aplified. There are two things that influence this:

  1. Size of sensor pixel: if you have 12 megapixels on 24×16 mm APS-C sensor, each photosite is smaller that it would be on say 2 megapixel APS-C sensor. Therefore is catches less light and needs more amplification. Similarly, 12 Mpix D90 sensor has significantly larger photosites than 12 Mpix compact camera sensor, and thus has less noise. This is one reason people buy DSLRs instead of compact cameras.

  2. ISO setting on camera. Basically, ISO says how sensitive you want the sensor be, so higher ISO means more amplification. You'll find that lower ISO settings produce less noise in images, and on D90 noise probably won't be noticable at ISO 200 or so.

Obviously, avoiding noise has it's drawbacks, because larger-sensor camera are bigger and more expensive, and using lower ISO might means either opening up aperture and losing depth of field -- provided that you have fast enough lens (fast lenses can also be expensive). The other option is longer exposure time that means risk of blur from camera shake or moving subjects.

Sometimes, as rfcusa notes, in 12 Mpix images certain amount of noise only matters when you're examining it in 100% magnification on a computer. Unless you intend to produce huge prints, these viewing conditions happen very rarely.

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Thanks! This was what I was looking for (minus the part about the sensor size, since I can't really replace or do anything about that :P). –  SpikeX Jan 20 '11 at 22:13
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Note, too, that thermal noise can be a big part of the equation -- for a given light level, a cooler camera will be less noisy than a warmer one -- and that "live view" can be a significant contributor to thermal noise in the sensor. Using the prism viewfinder (and it is a prism rather than a pentamirror on the D90) rather than the LCD for composition, etc., should further reduce noise, especially in long sessions. –  user2719 Jan 20 '11 at 22:18
    
I rarely use the Live View on my D90, I don't like it, I find it too slow for focusing and way too slow on the shutter speed (since it has to close first, and then re-open it). I always use the viewfinder. ;) –  SpikeX Jan 20 '11 at 22:29
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Most DSLRs are somewhat grainy at 100% digital zoom.

I use the same body and lens and the best thing you can do is set your ISO low (I keep mine around 200) to prevent noise. The D90 is also acceptable in noise up to 1600.

If you are having to digitally zoom on your computer to get the right composition you probably need a different lens. Maybe you should invest in a good telephoto lens like the a 70-200 2.8 or a teleconverter.

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I'm not zooming for composition, I'm zooming simply to view the quality of the image at its original resolution (not shrunk down). The amount of noise when viewing the image at its full resolution at 100% zoom was rather large, which is why I asked about it. –  SpikeX Jan 20 '11 at 22:00
    
Then what you are probably seeing is lens distortion. Its normal to have some degree of distortion at 100% zoom. There isn't much you can do about that except correct it in Lightroom/Photoshop. –  atodd Jan 20 '11 at 22:07
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lens distortion has nothing to do with noise, and you probably will not notice any of it at 100% view. –  ysap Jan 20 '11 at 22:39
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If you're shooting indoors, and not using flash, the kit lens is typically much to slow for many, many shots. Your camera (or yourself) is probably raising the ISO and this is noise due to the increased ISO. Either get flash, a faster lens, or shoot somewhere with more light.

A certain amount of this noise is present in many normal, high quality shots when viewed at 100% - depends strongly on sensor, light, and ISO. Unless you're printing at 100%, don't fall into the pixel peeping trap.

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So a better lens will help, but not by a lot? I figured as much. I've read online the stock D90 lens isn't really all that great... perhaps I'll invest in the Nikon 18-200mm lens... I hear it's much better for general-purpose shooting. I'll also tweak the ISO settings on my camera a bit, too, I didn't realize it had that much of an impact on the quality. Thanks. –  SpikeX Jan 20 '11 at 22:09
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ISO has quite a bit of an effect on quality, especially towards the upper range. A faster lens will help (faster meaning a wider aperture (lower maximum f stop)) because it will allow you to shoot without the need to raise your ISO more often. I don't believe the 18-200 is a faster lens. Your lens needs really depends on the kinds of shots you do. –  rfusca Jan 20 '11 at 22:13
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The D90 (and other cameras as well) has a feature that will automatically boost the ISO in order to get the correct exposure. If you turn this off, then you can set the ISO manually and thus cap the noise levels.

Of course, if you do this, you run the risk of not getting the correct exposure. But this is where a faster lens (as @rfusca mentions) helps.

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One thing that hasn't been mentioned so far is the effect of the software you use to import images. If you're shooting RAW, your RAW processor may be applying some sharpening to your images by default, which adds noise.

I know for a fact that Adobe Lightroom does this, very annoying when a super-sharp image suddenly looks noisy for no apparent reason. For Lightroom, this can be fixed by creating appropriate import presets, and I would imagine that most other RAW converters also have a facility to modify the default sharpening.

EDIT: As Francesco says below, if you're shooting JPEGs, you might get better results by reducing the amount of sharpening applied in-camera. I have no idea if this is possible specifically with a D90 though.

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Usually it's the other way around: the jpg coming straight out of camera has been automatically sharpened I an irreversible way, while the raw file is mostly untouched and you can decide if, how and how much sharpening apply. For this reason an unprocessed raw file will be displayed as a softer image than a "typical" jpg. –  Francesco Jan 2 '13 at 19:45
    
I recently had a really sharp image shot at ISO 100 which showed a lot of noise in LR, especially in the out of focus areas. Since this image had been shot specifically to get rid of the noise, I was not amused until I suddenly remembered LR's default sharpening. –  Chinmay Kanchi Jan 2 '13 at 20:03
    
I'm not sure to have understood, what you are saying is not in line with my experience with LR. Maybe you could ask a question about it with all the details so we can solve/clarify the issue in an adequate venue and not in these comments? –  Francesco Jan 2 '13 at 22:39
    
It's quite simple, really. Without any custom presets, LR applies some amount of default sharpening to the image. This may or may not be specific to camera model, but on images shot with a Canon 30D, the default sharpening settings are Amount: 25, Radius: 1.0, Detail: 25 and Masking: 0. This can introduce some (completely reversible) noise into images. –  Chinmay Kanchi Jan 2 '13 at 22:44
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now I understand, actually I asked a question about it some days ago. photo.stackexchange.com/q/30798/5032 :-) You are probably interested in the "Zeroed" setting which doesn't apply anything (as far as I know). –  Francesco Jan 2 '13 at 23:08
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The reason for visible noise is not enough light.

The description below is an inaccuratee simplification but it helps to undertake the issue.

There's always some level of noise, when you're photographing something nice and bright there's a lot of real data to overpower the noise.

When you photograph darker scenes the power of the real image is closer to the power of the noise and so the noise become visible

To see the effect just take a photo in direct sunlight and see there isn't much noise.

To reduce noise you should try to get more light into the camera - you can use a wider aperture (lower f number), longer exposure or add light (for example with a flash)

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Side note: Why has this question gotten 4 additional answers in the past few hours? Was it featured somewhere? This question is a year and a half old! –  SpikeX Jan 2 '13 at 21:31
    
Because it popped up on the front page for some reason. –  Chinmay Kanchi Jan 2 '13 at 23:47
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When the camera does not have sufficient light, it will usually compensate by increasing ISO (from a baseline of 100).

You can fix this by making sure your scene is well lit.

Your lens is faster when zoomed out, so zooming out and "zooming with your feet" will allow the camera to reduce ISO.

You could choose to underexpose to reduce ISO.

Consider setting "High ISO NR" to "High" in your camera settings.

Consider reducing the dimensions of the images your camera creates.

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