3 Digital noise: What it is
and how to deal with it
Pictures, regardless of how they are created and recreated, are
intended to be looked at. This brings to the forefront not the technol-
ogy of imaging, which of course is important, but rather what we
might call the eyenology (seeing).
—Henri Cartier-Bresson
Noise in digital photographs is the visual equivalent of static you
hear in radio signals, and most digital cameras add some level
of noise to images. In traditional photography, the nearest equiv-
alent is fi lm grain. Like fi lm, digital noise is noticeable in images
shot at high ISO settings, and more visible in areas of uniform
color, such as skies and shadows. Digital sensor noise may also
be increased when long digital exposures are made under low-
light conditions, such as night photography, and noise is always
more obvious in areas of underexposure.
Camera noise is spread across the frequency spectrum, and
includes fi ne and coarse components. Noise varies with color
and brightness, and it is different for every camera (or scanner
too), but blue-channel noise is usually higher than in other chan-
nels, and shadow noise is typically higher than brighter areas.
Too much image compression produces an effect that appears to
be noise but is really JPEG artifacts. This is an entirely different
