Spectral signal-to-noise ratio
In applied mathematics, the two-dimensional Spectral signal-to-noise ratio measures the normalised cross-correlation coefficient between several two-dimensional images over corresponding rings in Fourier space as a function of spatial frequency. It is a multi-particle extension of the Fourier ring correlation, which is related to the Fourier shell correlation. The SSNR is a popular method for finding the resolution of a class average in cryo-electron microscopy.Calculation
where is the complex structure Factor for image k for a pixel at radius. It is possible convert the SSNR into an equivalent FRC using the following formula:
