Why and how small pixels influence the image quality

Started Mar 31, 2012 | Discussions thread
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schwoofi
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Why and how small pixels influence the image quality
Mar 31, 2012

http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/

Example Nikon D3s vs D800 at ISO 25600

http://www.sensorgen.info/NikonD3s.html
http://www.sensorgen.info/NikonD800.html

Nikon D3s

12MP
Saturation = 743
Photon noise (18% grey) = sqrt(743*0.18) = 11.6
Read noise = 3.2

SNR (18% grey) = (743*0.18) / sqrt( 11.6² + 3.2² ) = 11.1 = 20.9dB (DxO=20.8)
DR = log2( 743 / 3.2 ) = 7.9 (DxO=7.63)

Nikon D800

36MP
Saturation = 252
Photon noise (18% grey) = sqrt(252*0.18) = 6.7
Read noise = 3.7
SNR (18% grey) = (252*0.18) / sqrt( 6.7² + 3.7² ) = 5.9 = 15.4dB (DxO=15.2)
DR = log2( 252 / 3.7 ) = 6.1 (DxO=5.91)

Scaled to 12MP
Saturation = 3*252 = 756
Photon noise (18% grey) = sqrt(756*0.18) = 11.7
Read noise = sqrt( 3* 3.7² ) = 6.4
SNR (18% grey) = (756*0.18) / sqrt( 11.7² + 6.4² ) = 10.2 = 20.2dB
DR = log2( 756 / 6.4 ) = 6.8 (more than one stop lower than D3s)

(The DxO measurements, when scaled to 8MP, are SNR=21.8, DR=7)

Conclusion

There definitely is an effect, even if scaled down.

Smaller pixels negatively affect DR and the SNR. The latter in darker areas mostly.

Best regards

 schwoofi's gear list:schwoofi's gear list
Sigma DP1 Merrill Sigma DP3 Merrill Canon EOS 5D Mark III Canon EF 50mm f/1.4 USM Canon EF-S 18-55mm f/3.5-5.6 +4 more
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