This article should be read by everybody

Started Dec 12, 2013 | Discussions thread
lhkjacky Senior Member • Posts: 2,807
Re: Sony a57 vs A77 Proof that Pixel Count Affects Noise

K E Hoffman wrote:

Similar technology, same sensor size. MORE PIXELS CREATES MORE NOISE because the signal output of the pixels is less but there are fixed noise contributors. So more pixels in mid to lower light areas will be about noise not the shot. Images with areas of dark will show noise there.. so if you don't live in a HIGH KEY world. there is a Noise Cost


With the same sensor technology, smaller pixels does create more noise.

For example, a 5×5 µm pixel can collect 4000 electronics, while

four 2.5×2.5 µm pixels can collect 1000 electronics each.(4000 in total)

However, there are always background noise, electronic noise, thermal noise, etc. which cause +/-50 electronics noise per pixel due to the wiring, or nearby electronic components.

Large pixel: 4000 +/-50

Small Pixel:1000 +/- 50 (4000 +/- 200)

So larger pixel does have better Signal to Noise Ratio.

The reason is also written in the article .

At some point, pixels become so small that the assumed idealized scaling (with an assumed constant fill factor and constant “quantum” efficiency) will no longer apply: four 2.5×2.5 µm pixels together would capture less light than one 5×5 µm pixel (because of wiring that gets in the way, mechanical overlay tolerances on filters, “fill factor”, etc). The resulting decrease in signal-to-noise ratio would negatively impact the DxOMark Camera Sensor score.

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