The discriminator as to whether this technique works or not is in how
the manufacturer of a specific camera has implement ISO
configuration. Basically, the sensor has a baseline ISO, the result
of its construction, photosite area and physics. You can get a higher
ISO by amplifying the sensor's gain (precisely how you do that I am
not sure as I'm not an electrical engineer... ) or by multiplying the
captured data values, or a combination of both.
I tried it on a couple of different cameras a year or so back. It
gave slightly better results on one camera, much worse results on
another, etc.
For my purposes, better to just use the camera as the manufacturer
intended and learn how to set exposure to minimize noise... ;-)
Godfrey
On Apr 23, 2006, at 7:59 PM, Shel Belinkoff wrote:
Over the last couple of days I was thinking about noise that's
generated in
digital photo files, and was wondering if longer exposures at lower
ISO
gave more or less noise than a shorter exposure at higher ISO ratings,
assuming the overall exposure is the same in both instances. It
seemed
like a good idea for some testing.
Now, just a few minutes ago, I came across this comment:
I believe (he) means that he's set the camera at
ISO 400 and then (using the exposure
compensation feature) deliberately underexposed 2
stops... thus yielding the same exposure as if the
ISO had been set to 1600 to start with. Then, plus
two stops of compensation is applied during
"development" (the conversion of the RAW data)
[...]
With some digital systems [...] it tends to yield
a bit more noise (the digital equivalent of grain)
than with the (camera's) native ISO 400 setting,
but much lower noise than obtained by
using the (camera's) native ISO 1600 setting.
So [...] it's a way of increasing the quality of shots
at higher ISO's.
Well, I'm no expert on such matters, but I tend to believe what I
see, so i
did a quick test. Unfortunately, the light was changing rapidly,
and it
might be better to try this when the light is more stable.
However, this
first Q&D experiment seems to indicate that lower noise is
observable using
this technique. But don't take my word for it, try it yourself under
stable lighting conditions, and see what results you get.
Shel
