macrobild
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Här kommer en text som sätt förklarar lite vad vi har talat om tidigare, en given sensoryta och olika antal pixlar .
The main reason why denser sensors aren't noisier is that in modern sensors the gaps between each sensor site ('sensel') have been minimised to a level where their effect on output is negligible. As a result, the sensels effectively cover the entire sensor area, regardless of how many or few of them there are. Consequently the light-gathering power of the sensor is entirely dependent on its surface area, and very nearly independent of how finely that surface area is divided up.
The noise of reading the dearth of photons striking the sensor in near darkness is fairly random, and therefore it averages out to nothing over a large number of pixels. Imagine 10 Mpixel and 40 Mpixel sensors of the same size. Each sensel on the 10 Mpixel sensor will take up the same area as four sensels in the 40 Mpixel sensor, and each sensel from the 40 Mpixel sensor will be a quarter the size of the sensels on the less dense sensor. The four smaller sensels will be noisier, individually, than the one large sensel. Let's say for the sake of argument that they are each four times noisier. However, in producing a 'downrezzed' 10 Mpixel image from the 40 Mpixel sensor, the values of the four small sensels are averaged together, and the variation of their noise averages out between the four. Each sensel may be four times noisier than the larger sensel, but once averaged together, the value of the composite four-in-one sensel will be no noisier than the larger sensel. In this model, while noise varies per sensel as sensel size changes, the noise per square millimetre of sensor doesn't change. That applies to pixels in the final image too. In any given area of the final image, read noise does not vary significantly with density of sensels.
The main reason why denser sensors aren't noisier is that in modern sensors the gaps between each sensor site ('sensel') have been minimised to a level where their effect on output is negligible. As a result, the sensels effectively cover the entire sensor area, regardless of how many or few of them there are. Consequently the light-gathering power of the sensor is entirely dependent on its surface area, and very nearly independent of how finely that surface area is divided up.
The noise of reading the dearth of photons striking the sensor in near darkness is fairly random, and therefore it averages out to nothing over a large number of pixels. Imagine 10 Mpixel and 40 Mpixel sensors of the same size. Each sensel on the 10 Mpixel sensor will take up the same area as four sensels in the 40 Mpixel sensor, and each sensel from the 40 Mpixel sensor will be a quarter the size of the sensels on the less dense sensor. The four smaller sensels will be noisier, individually, than the one large sensel. Let's say for the sake of argument that they are each four times noisier. However, in producing a 'downrezzed' 10 Mpixel image from the 40 Mpixel sensor, the values of the four small sensels are averaged together, and the variation of their noise averages out between the four. Each sensel may be four times noisier than the larger sensel, but once averaged together, the value of the composite four-in-one sensel will be no noisier than the larger sensel. In this model, while noise varies per sensel as sensel size changes, the noise per square millimetre of sensor doesn't change. That applies to pixels in the final image too. In any given area of the final image, read noise does not vary significantly with density of sensels.
