In scientific imaging, the two-dimensional spectral signal-to-noise ratio (SSNR) is a signal-to-noise ratio measure which measures the normalised cross-correlation coefficient between several two-dimensional images over corresponding rings in Fourier space as a function of spatial frequency.
[1] It is a multi-particle extension of the Fourier ring correlation (FRC), 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.
is the complex structure factor for image
It is possible convert the SSNR into an equivalent FRC using the following formula: