56 Better Available Light Digital Photography
problem, but one that may have a similar solution. (See “Noise
Comes in Different Flavors.”) Digital cameras with physically
larger sensors (not just more megapixels) tend to produce less
noise than do those with smaller sensors. This is because the size
of the chip allows larger pixels to absorb more light.
If noise is the problem, digital noise reduction (DNR) is one of
the software solutions. Most of today’s noise-reduction software
relies on wavelet theory, which is a mathematical method that
allows the software to identify and suppress noise at different
frequencies, locations, and color channels. There are lots of dif-
ferent noise-reduction products available for Mac OS and
Windows computers. Joe has tested many of them, and here’s a
short list of useful products in order of my preference. Keep in
mind that your camera and the kind of images you make may be
different from mine or Barry’s, so download a demo version of
any of these products that sound interesting and give them a try.Noise Comes in Different Flavors
Like fi lm grain, digital noise has many causes: Dark noise comes from heat produced in the camera’s sensor during
image capture. The dark current created ends up being collected along with the data from light passing through the
lens. Random noise is created by fl uctuations within the camera’s circuitry or even from electromagnetic waves
outside the camera. Signal noise is caused by fl uctuations in the distribution of how light strikes an image sensor.
You’ll sometimes hear the term signal-to-noise ratio, which is a measure of signal strength relative to background
noise. Amplifi ed noise is caused by high ISO speeds, and is the digital equivalent of chemically “pushing” fi lm in order
to achieve greater light sensitivity. Then there’s accumulative noise, which is caused by using slower shutter speeds.A good tripod (see Chapter 6)
must be steady enough to allow
exposures that are not only long,
but less noisy as well. Camera
was a Canon EOS 1D Mark II
at ISO 200 with an exposure of
ten seconds at f/20 in Manual
mode and ISO 200. © 2005 Joe
Farace.