Pixel Binning
Combining the signal from several adjacent photosites into one output pixel to improve signal-to-noise ratio.
Formula / rule
SNR gain ≈ √n
Measured in
× (2×2, 4×4)
In depth
Binning four photosites into one quadruples the collected signal while the random noise only doubles, giving a net gain of one stop at the cost of three-quarters of the resolution. Phone sensors with very high nominal pixel counts rely on it constantly, shooting binned in low light and full resolution in daylight.
Examples in practice
A 48-megapixel phone sensor outputs 12-megapixel files at night, binning four photosites into each pixel.