Tim Randles wrote:
> Thanks for the detailed explanations, although I am a big baffled by some of
> the terminology.
>
> What is "noise?"
Tim:
To expand a bit on Chuck Norcutt's explanation, there's "data" and
there's "noise," and, in the context of a photo, "data" is a
more-or-less accurate representation of an image's brightness and colour
values by each image-capturing pixel on an imaging chip, whereas "noise"
is an inaccurate (sometimes *wildly* inaccurate) representation.
So, as Chuck intimated, a "noisy" imaging sensor will display a lot of
random coloured (and randomly-bright) pixels in an area of the image
that was *supposed* to be relatively dark and featureless, such as a
deep shadow. You can minimize this effect by setting your ISO to manual
and its lowest setting (typically 50 or 100 ISO).
Canon's reputation for having low-noise imaging chips is becoming
legendary -- in this respect, Canon's the 600-pound gorilla in the room,
and the standard to meet or beat by competitors now and in the future.
Some people ascribe this relative lack of noise to the fact that Canon
uses an imaging technology with the acronym CMOS (Complementary
Metal-Oxide Semiconductor), whereas most of the competition uses CCD
(Charge-Coupled Device) technology. Canon's technology is also largely
in-house -- they make their own imaging sensors, rather than sourcing
them from third parties.
However, there's technology and there's technology. Fuji (for instance)
uses CCD, but their imaging sensors are actually considered to be fairly
low-noise. This is due in part to the choice of chip (there's a variety
of CCD chips out there and they have differing characteristics) and part
to the amount and type of post-processing that the camera's smarts do to
the image after it leaves the chip and before it gets stored in memory.
Most professional astronomers used (and still use) CCD imaging, though
they sometimes do some fairly exotic things to maintain image quality
(such as cool the chips using liquid nitrogen or some other cryogenic
technique). Cooling the chip also helps keep noise down. (As a related
note, my KonicaMinolta A1 takes generally excellent pictures, but I and
others have noticed that, if we leave the camera on for long periods of
time, the guts heat up, and the resulting images get noisier the warmer
the innards of the camera are.)
The Holy Grail is a noiseless chip, but this is impossible due to
constraints of physics. (It was also impossible with film, BTW.) The
more post-processing that is done to a noisy image, the more "plastic"
the resulting image seems to appear. The Four-Thirds System is reputed
to have something more of a handicap than other imaging formats/sizes,
because a smaller imaging chip needs to pack more pixels into a smaller
space, and the pixels themselves need to be smaller and closer together,
in order to get the same megapixel count as their competition. Both of
these strategies tend to increase image noise.
Like most things in life, choice of camera system is a series of
trade-offs/compromises. If you *really* like a compact SLR system,
you'll stick with something like Four-Thirds (which is what the
E-thingies of Olympus are), whereas if you're really hyped about getting
low-noise imaging, Four-Thirds will not be your first choice. Right
now, I suspect that choice would almost always be Canon, though things
could change in the future.
Garth
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