More megapixels, better photos: Fact or fiction?

Started Feb 7, 2008 | Discussions thread
cpw Regular Member • Posts: 313
Re: So many misinformed replies

ejmartin wrote:


While the individual parcels have more
variance, since a fixed area of sensor has the same number of photons
falling on it, a fixed area of the image still has the same number of
photons and thus the same sample variance and hence the same noise on
a per area basis. The only thing that more pixels brings is more
resolution, and that's a good thing.


Such a general statement as this, i.e. per area noise equality, only strictly holds if there is only shot noise. However, each pixel has read noise on it, it has to taken in to account (I know you talk about read noise below).

To see this, look at an extreme case. Suppose 10,000 e- hits an area patch. One camera has 1 pixel for this area, and a second camera has 10,000 pixels. Both have 20 e- read noise. The SNR for the area in the first camera would be 98. The SNR for the second camera would be about 5, because you have to rss the noise contributions (which in this case is read noise dominated for the second camera) from all of those little pixels.

Now you might say, well I chose a hypothetical situation, which I did, to show this point: that you can't just make this general statement, that per area we get the same noise, irregardless of pixel size, and only use shot noise to prove it.


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