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Old Aug 9, 2004, 11:28 AM   #1
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I have read a reply to a posting in another section stating that more megapixels can actually give you a poorer quality image in the size of the CCD is not increased.

To what extent does more pixels lower the image quality? For example, would the Canon S410 produce better pictures than the S500, or the Casio EX-Z30 produce better pictures than the EX-Z40?

Are there any guidelines for megapixel to CCD size ratio?
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Old Aug 11, 2004, 8:14 AM   #2
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CCDs create heat...heat creates noise...more pixels on the same sized CCD mean more heat that *can* be generated. There's no math formula, just reality.

Also, there's nothing that states that one camera with a larger CCD or less pixels than another will have a better image quality...just that if you try to pack more pixels onto a CCD there's more *chance* for noise as you continue to use the camera or shoot long exposures.

For the best pictures, you can get a dSLR with a full frame CCD (same size as a frame of 35mm film)...but you're paying a lot of money for one of those.
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Old Aug 11, 2004, 10:40 AM   #3
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The noise reduction from larger pixels is not just heat. What really matters is the signal/noise ratio - with larger pixels there is more light falling on each pixel (photo element?) so more signal. I'd also expect the noise to increase since there is more material (semi conductor thingies) to generate the noise. Given the square root that always sneeks into those discussions, I'd expect the noise to go down linearly with the increaase in size of the "pixel".

In addition, there have to be quantum mechanical edge effects going on. Since the edge/area ratio decreases as the sizee of the "pixel" increases, so should the randomness of the quantum edge effect.
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Old Aug 11, 2004, 2:49 PM   #4
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Everyone is correct... some heat, some photon, some amplifiers, some dark current etc...! :-)

I came upon this write up a while back describing all the noise sources from the experts: http://www.genesis16.net/Kodak/CCD%2...%20No.%201.pdf
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Old Aug 11, 2004, 3:56 PM   #5
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And you might be interested in this imager size chart to see how many different sizes there really are out there ... it's a little dated now and does not include some of the newer chips but it's still good reference.

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