Maybe I'm a cynic. Having been an analog CMOS IC designer for years,
familiar with all the A/D linearization and calibration schemes. The ultimate
limit is the core electronics. I look at places like dpreview, which attempt to
be as objective as possible, but they measure and compare camera noise
based on a constant area of tone; and I know there are a lot of post processing
techniques that can be done, so the numbers don't mean much. Consider,
for instance, the disclaimers that said the pre-production olympus E-1s did
not have the full noise reduction algorithms working and hence were not
valid in comparison to other cameras. Just implies that one can tweak the
camera software to improve whatever you look at, so the numbers just end
up being engineering tradeoffs between various algorithms.
Like I said, if one could look at the purely raw electronic data and see
what the underlying electronics can actually do before any processing,
maybe a realistic comparison could be made between cameras. I find
it hard to believe that a camera with a pixel sensor half the size of another
camera could have the same or better noise performance, unless there was
some other performance tradeoffs being made. So one camera has higher
noise but a sharper image. You don't really know if you are just seeing the
difference in post-processing algorithms.
OK, I've had my rant. Crank those babies up to iso 1600 and see what they
can really do.
At 12:45 PM 9/21/2003, you wrote:
><snip>
>A good measurement is to photograph a uniformly-lit surface (which need not be
>gray) and compute the average and standard deviation of the values of the
>pixels in a patch containing at least 50 pixels. Do this computation three
>times, once per color. The larger the ratio of the standard deviation to the
>average the greater the noisiness of the image. This is a standard way to
>measure such things.
Like I said, this is exactly the kind of test that can be manipulated most by
post
processing in the camera. You have no idea what happened to any potential
detail that would have existed in a real photograph over that same area. If
there
is no detail, any camera can average out the noise and you would not know the
difference. We need a noise test that contains detail also, like a real
photograph.
Wayne
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