Nearly all digital cameras today offer many high ISO options, with sensitivity levels up to ISO 1600, ISO 3200, or even higher. These are very useful, since they allow us to shoot at a faster shutter speed in a dark location as discussed in Photo Tip of the Week: Low Light Photography. Set ISO 3200 inside a dark theatre for example, in order to shoot at a shutter speed of around 1/60 sec. That will minimize the risk of blurry photos caused by camera shake or the actors' movement. Granted, image quality does suffer at very high ISO levels, but there are some ways to minimize that problem.
The photo at the top of this story was taken at ISO 3200, with noise reduction turned off. I did this to make a point: If digital cameras did not provide noise reduction processing, high ISO images would be extremely "grainy" with obvious colour speckles.
Digital Noise Issues
Any digital camera's sensor is designed with a "native sensitivity," typically ISO 100 or 200, and we get the best possible results at that level. In order to allow for shooting at higher ISO, the camera can instantly boost the effective sensitivity of the image sensor. That's done by amplifying the signal output. This allows for shooting at high ISO levels; but the more the signal is amplified, the more obvious the digital noise will be. The coloured speckles (caused by electronic interference) can create a very grainy-looking effect.
In order to make the digital noise pattern less visible, cameras applies noise-reduction processing. That works by blurring the digital noise pattern so the speckles are not as colourful or as sharp. Newer cameras use more sophisticated Noise Reduction (NR) algorithms than older models, but the extra processing still blurs fine details to some extent. That can reduce the definition of intricate detail in the image, especially with cameras that use aggressive NR processing.
If your camera's menu includes an item for High ISO Noise Reduction (NR), consider setting it to a slightly lower level than the default. This will make digital noise more visible, but the definition of fine detail will also improve. Take a few test shots at ISO 3200 at the default NR level and at the lower NR level. View both photos on a computer monitor at 100% magnification to decide which you prefer.
Note: It might be tempting to use a very high NR level to eliminate digital noise for a very smooth image. It's worth experimenting with that too, but the results will probably appear "mushy" or "plasticky": excessively smooth.
The photo at right has had a grossly excessively level of Noise Reduction applied (achieved with software for this illustration). This results in a very smooth image but blurs intricate detail and produces an artificial-looking effect.
Software Solution (JPEGs)
If you're willing to spend extra time on each photo in a computer, programs such as Nik Dfine 2 ($100) noise reduction software let you fine-tune JPEG images (It works well when in-camera NR was set at Off or Low but that's not necessary.) Try the free trial download first; you'll find it to be very versatile in controlling the level and type of noise reduction. Be sure to view the image at 100% magnification on your monitor while adjusting the NR levels.
As the photo at left shows, setting in-camera Noise Reduction to a level just below default provides a photo with some visible digital noise but the fine details remain well defined. This photo would be ideal for fine-tuning with sophisticated Noise Reduction software.
Software Solution (RAW)
If you shoot in the RAW format, use a versatile RAW converter program with a full set of tools for Noise Reduction. After modifying exposure, colour, etc., set the desired level of NR and sharpness that provide the effect you personally prefer. Then convert the photo to the TIFF format. (For more information about RAW format and the software, see Photo Tip of the Week: Take Advantage of Raw Capture Mode.)
All cameras that provide a RAW capture mode ship with software for modifying and converting such photos. Of course, some of these programs offer little or no control over Noise Reduction. Very versatile options for RAW photos include the Adobe image editing programs, Nikon's pro-grade Capture NX2 for Nikon owners ($250), Photo Ninja ($129) and DXO Optics Pro ($170) which is my favourite RAW converter when testing many cameras, Try the free trial download of at least two of these programs. Experiment to find the one that you personally find most intuitive to use and the most versatile.
The Bottom Line
Frankly, the best bet when shooting in a dark location is to use a solid tripod and shoot at a low ISO level for the best image quality and sharpness. Of course, digital noise can also be problematic (though less so than at very high ISO) with an exposure that's much longer than two seconds. And a tripod cannot eliminate blurring caused by camera movement. As well, you won't always be ale to use a tripod. In either situation, set a high ISO for a fast shutter speed, and get the best possible quality with the tips provided in the Solution sections above.
And remember to always check the ISO that's set before you start taking photos. No matter how long you have been using a digital camera, you'll sometimes forget to change your ISO level. After shooting at night without a tripod, you may begin shooting on a sunny morning at ISO 3200. That won't be a crisis, but you certainly won't get the best images your camera can provide.