Contrary to conventional wisdom, higher resolution actually compensates for noise

Sunday November 16 2008

Sensor Insight
Introduction | Modeling small pixels | Comparing the SNR of cameras with different resolutions | Real-life comparisons | Conclusion

The argument above provides a method to compare cameras with different resolutions. A high-resolution camera can still be turned into a low-resolution camera by averaging its pixels.

In order to compare all cameras and not just pairs, a reference resolution can be chosen and equivalent SNRs at this resolution are computed. Let Nref denote this reference resolution. Consider a camera with N Mpix. To obtain an image with Nref pixels, N / Nref pixels need to be averaged out to produce a single pixel in the output image, so the noise decreases by a factor of . We then deduce that SNRref at resolution Nref can be obtained from the nominal SNR (in dB) using the formula

Notice that if the reference resolution Nref is very large, or if the initial sensor has a low resolution, the normalized SNR can actually be lower than the nominal SNR.