Pixel density - can the playing field be leveled???

Started Jun 6, 2009 | Discussions thread
Steen Bay Veteran Member • Posts: 7,418
Re: 10mp vs 20mp

Steen Bay wrote:

Cheburashka wrote:

Steen Bay wrote:

P.S. - Actually it isn't quite correct to say that the image level shot noise is the same regardless of pixel count. That assumes a 'perfect' downsampling of the 20mp image to 10mp. The 'constant noise' argument is only valid when comparing at the same 'spatial frequency' or resolution. As it is, with its higher resolution, the 20mp image has 41% higher 'image level' shot noise, since the signal is the same for the sensor as a whole, and the sum of the per pixel shot noises is 41% higher.

If we are comparing two systems on the basis of noise performance, then it only makes sense to do so at the same level of detail. To do otherwise artificially penalizes the more detailed image since the extra detail could be traded for less apparent noise via NR (noise reduction) and/or downsampling.

Regardless, there still isn't more photon noise in the 20 MP image. It's just that the noise is resolved more clearly, so it's more visible. The 10 MP sensor blurs the noise that is already there, just as it does with the detail, which gives the impression that there is less noise, even though the noise content is the same.

Yes and no. I don't really buy the argument that the noise is already there in the lower resolution image, that we just can't see it! It's a bit like saying that above the clouds the sun is always shining. It doesn't really help much. Higher resolution is a nice thing, but it comes at the cost of more noise. It's a trade, no reason to hide that. And won't a 20mp G11 have one stop less DR that can't be recovered with downsampling? (and still I'll probably get the 18mp 7D ;-))

P.S. - Then I said above that the hypothetical 20mp G11 would have 41% higher per area read noise if the per pixel read noise was the same as on the 10mp camera.. that was compared to the case where the per pixel read noise was scaled (down) with the pixel size. So, on top of the one stop (41%) higher per pixel (and 'per area') shot noise and one stop lower DR (that's the result of twice as many pixels) comes the effect of a 41% higher read noise (relative to the signal and shot noise) if the read noise isn't scaled on the 20mp camera, and then the one stop difference in the highlights would grow higher and higher when mowing down towards the deep shadows, where the relatively higher read noise becomes more important. (Well, at least I think so. This is really a bit confusing! ;-))

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