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PostPosted: Mon Jun 11, 2007 6:38 am 
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Joined: Thu Jun 07, 2007 10:15 am
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Hi all,

I have one question. Maybe you can help me with it. I recently bought a DSC-N2 from Sony. As you all know it uses a 1/1.7" CCD with a 10MP resolution.
So if I am now not using the full 10MP resolution, but i.e. only 5MP, does the camera use the additional 5 redundant megapixels in order to improve the Signal to Noise ratio. In other words, can I use higher iso values without running into danger of further increasing the noise if I am using lower resolutions of the camera?

Thank you very much for your answers,

Peter


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PostPosted: Mon Jun 11, 2007 8:16 am 
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Hi Peter, that's a great question, but one I can't answer as I don't have the N2 in front of me. Many cameras use a technique known as 'pixel-binning' where lower resolutions are used to allow groups of pixels to act as one extra-sensitive super-pixel. This could increase sensitivity (or decrease noise).

The thing to weigh up though is a low noise but low res image against a higher noise, but high res image. Remember at higher resolutions, the noise artefacts are smaller on a print made the same size and therefore normally more discreet.

Also, if you were to use four pixels as one bit pixel, you wouldn't be talking about halving the number of megapixels. For example, the N2 has 3648 x 2736 pixels, so halving it in each axis to allow a 'quad-pixel' would produce images with 1824 x 1368 pixels. That's actually about 2.5 Megapixels.

So clearly to gain much benefit from pixel binning, you need to greatly reduce the working resolution, which could be too much of a compromise.

Of course this is all theory, so how about some practice? Peter, I know you came here looking for answers, but you're actually in the perfect position to provide them!

Could you take two photos straight after each other of the same subject at, say 800 ISO. If you can, do it on a tripod and use the self timer to take the shots. A photo indoors would be perfect.

Do one at 10 mpixels and the other at 5mpixels and post them here (or on flickr) for us to have a look at and compare...

Cheers!

Gordon


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PostPosted: Mon Jun 11, 2007 7:31 pm 
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Nice test! I'd like to see the results.
But unfortunately the outcome surely depends on the algorithm of the in-camera processing.
My suggestion in any case would be: Always shoot in full resolution and apply some high-quality de-noiser in software afterwards if you think that's necessary. In that case you have more freedom, because lost resolution can never be brought back to the original shot :idea: :!:

P.S.: keep in mind that setting the cam to lower resolution will not really decrease the noise of a single optical cell :(

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