http://www.digitalcameraworld.com DECEMBER 2019 DIGITAL CAMERA^55
CAMERA COLLEGEDifferent types of noise
Noise manifests itself in some distinctive ways, according to the camera settings
There are essentially two
types of noise to deal with
in digital photography:
luminance (or greyscale) and
chroma (or colour). The latter
is more objectionable, as it
covers an image in a galaxy
of coloured dots, blotches
and bands. Thankfully, it is
also easier to reduce without
taking a hit on image detail
in the way you do with
luminance noise reduction.Controlling noise
The camera features and functions that make a difference
Image processing
In-camera noise
reduction comes in
two flavours: high-ISO
and long-exposure.
Each can be applied
during the image-
processing stage,
before a picture is
saved to the memory
card, although long-
exposure noise
reduction requires an
extra shooting step.Shadows
Less picture information
is recorded in the dark
parts of a picture, so
the signal-to-noise ratio
is lower in these areas.
Attempting to recover
detail in the shadows
by brightening them in
software means that
noise is exacerbated
too. To avoid this, you
could take several
different exposures
of the same scene
and combine them.ISO
Noise becomes
obvious at higher ISO
speeds, although the
threshold for when
it starts becoming
unacceptable varies
between cameras.Long exposures
Heat can build up in the camera
during a long exposure, which
can produce thermal noise. It is
particularly noticeable when
you’re shooting exposures of
30 seconds or longer with your
camera’s Bulb mode, or if
you’ve been shooting video
before taking a picture. Some
cameras warn you that they
are getting too hot before
they automatically shut down.Sensor size and pixel density
All things being equal, a larger sensor produces less noise
than a smaller one: the light-gathering pixels are larger,
allowing them to capture more light for a higher signal-
to-noise ratio, and to dissipate heat more effectively.Noise is ulitmately unavoidable, but there
are several ways that you can lessen its
impact on the quality of your pictures...High-ISO noise
As the sensitivity is raised, the
amount of both salt-and-pepper-
style luminance noise and colour
noise is also increased.Long-exposure noise
In addition to noise created by
the build up of heat, you often
see ‘hot’ or stuck pixels in the
same position in your pictures.Banding
Just the worst! It can appear as
a thick strip of pixels, shown here,
or multiple vertical or horizontal
‘scratches’ in the shadows.