Q Looses the 3-D of the M?

Started Jul 23, 2014 | Discussions thread
Futax Senior Member • Posts: 1,170
Re: Q Looses the 3-D of the M?

MrSkelter wrote:

Actually downsizing has no effect on noise. That's a myth not supported by maths. You'll have all the noise just fewer pixels. It's easy to work out even if you don't do the calculations.

THOUGHT EXPERIMENT: You take a picture with the lens cap on using a hugely noisy camera at high ISO. The file looks like white noise but should be black as there was no light. You downscale that "snow" to a single large pixel. Is that pixel black or grey? It's grey. All the noise is still there.

But it certainly affects signal to noise ratio, which is what's important.  A thought experiment: downsize 16Mpx to 4Mpx.  You've effectively made each pixel 4x the size.  The signal adds arithmetically, the noise is adds as the square root of the sum of the squares.  So the signal increases by 4, the noise by 2: the signal to noise ratio has doubled.

This is exactly the same effect as quadrupling the pixel size (i.e. a 4Mpx sensor of the same size).

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- Keith.

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