More and more digital SLRs are offering higher ISO setting and along with the good news comes the bad. Noise in digital photographs is the visual equivalent of that static you hear in radio signals and most digital cameras add some level of noise to images. Like film grain, digital noise has many causes: Dark noise is produced by heat produced in the camera’s sensor during image capture. The dark current produced ends up being collected along with the data from light passing through the lens. Random noise is created by fluctuations within the camera’s circuitry or even from electromagnetic waves outside the camera. Signal noise is caused by fluctuations in the distribution of how light strikes an image sensor. You’ll sometimes hear the term signal-to-noise-ratio ratio, which is a measure of signal strength relative to background noise. Amplified noise is caused by high ISO speeds and is the digital equivalent of chemically “pushing” film in order to achieve greater light sensitivity. Then there’s accumulative noise, which is caused by using slower shutter speeds.
All of these factors combine so that some nighttime photography involves trial and error. While photographing cruise night on the main drag on Escondido California, I kicked the EOS 50D’s ISO setting up to 800, set the camera in Aperture Priority mode, chose an aperture and just lived with the 0.3 second exposure because I was more concerned about the mood of the shot that capturing these street rods in sharp focus. I made several shots experimenting with the Exposure Compensation control and for this shot increased by one-third stops, but the image was still slightly underexposed.
Both Adobe Photoshop and Lightroom have built in noise reduction features and for some shooters that may be all they need. If you need more, it’s time to bring out the power tools. Power Tools are small bits of software that can be Photoshop-compatible plug-ins, Photoshop Actions, or graphics utilities that make a digital photographer’s life a little easier for creating practical or special effects. Much like a an electric screwdriver makes household projects faster than an old-fashioned hand tool, software power tools, such as Nik Dfine (www.niksoftware.com) noise reduction tool let you produce imaging projects quicker and with less fuss, than doing it “the hard way.”