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Re: [OM] New E-1 (noise reduction)

Subject: Re: [OM] New E-1 (noise reduction)
From: "C.H.Ling" <chling@xxxxxxxxxxxxx>
Date: Mon, 22 Sep 2003 21:26:43 +0800
I think you have missed the point, it wa talking about compare camera noise
of different camera especially by checking the data on the DC test web site.
Since all DC process data differently it is hard to make a direct
comparision by the standard deviation data posted. Some camera is very
agressive in sharpening like C5050 and some are not like S1/2 Pro if the
tests were performed at the camera's "normal" setting it won't tell too
much.

C.H.Ling

----- Original Message ----- 
From: "Joe Gwinn" <joegwinn@xxxxxxxxxxx>

> >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.
>
> I don't think it's impossible to test such cameras, even if the internal
raw A/D counts are not available.  One test occurs to me right off:  With
camera on a tripod, take multiple picutures of the same scene.  Align the
images (if needed) and subtract them, pixel by pixel.  What's left is twice
the noise power in the individual images.  Do this with a collection of
scene types, including ones with large flat areas.  This is a classic
black-box test, is directly relevant to practical use, and cannot be evaded,
no matter what the camera manufacturer does.
>
> I know it sounds odd that subtraction of images yielded a doubling of
noise power, but that is correct, a consequence of the conservation of
energy.  The key is that the random noise is by definition different in the
two images, so it does not cancel out.  Only the non-random stuff (image
plus fixed-pattern noise) cancels out.
>
> The full strength version of this test is to process the images as
follows:  For each aligned pairs of images, compute the sum and the
difference images.  Divide each pixel in the difference image by the square
root of two, and in the sum image by two.  Then, divide each (reduced) pixel
in the difference image by the corresponding (reduced) pixel in the sum
image, yielding the per-pixel standard deviation of the image's random
noise, expressed as a fraction of the average value of each pixel.
>


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