62 Better Available Light Digital Photography
On-chip noise comes in two fl avors: Fixed-pattern noise is pro-
duced from uneven signal boost among different pixel amplifi ers,
and random noise occurs when shooting at different times of the
day. Random noise is typically suppressed when the sensor resets
the photodiodes that store electrical charges. Some digital SLRs
provide a user-selectable noise-reduction function that attempts
to eliminate this noise after the fi le has been written, sometimes
at the expense of fi ne detail. That’s because even though many
think the sensor is the key to image quality, its signals are totally
unrecognizable as an image until they’ve been gathered and pro-
cessed. That’s why some digital imaging processors prevent
noise from occurring in the processing stage. The noise that
remains is only the noise actually produced by the sensor.
More power creates more heat and noise. CCD sensors also
have increased power consumption at longer shutter speeds;
more electricity fl owing means, again, heat and noise problems.
Because of the literally millions of photodiodes and amplifi ersThis photograph made on The Strip in Las Vegas was captured with a Canon PowerShot SD10 digital point-
and-shoot camera that has a small imaging sensor, so noise should be a big problem, right? Nope. A combi-
nation of the built-in noise suppression, low ISO, and moderate 1/8 sec at f/2.8 exposure produced surprisingly
low noise. © 2004 Joe Farace.