pwspy.utility.DConversion.sigma2DApproximation(raw_rms, noise, NAi)[source]

Converts d_size to D using a 15th degree polynomial approximation of the sigma2D function. This function can be significantly faster than sigma2D but is not guaranteed to be accurate especially at extreme input values.

  • raw_rms (ndarray) – An array of RMS values you wish to convert.

  • noise (float) – A positive value indicating the background noise in the system in terms of RMS (E.G. the RMS of a measurement of clean glass). On the Backman lab “STORM” system this has been previously found to be 0.012. For the “LCPWS1” system it has been found to be 0.009.

  • NAi (float) – The illumination numerical aperture (NA) of the objective.

Return type



An estimation of D calculated from Sigma. It’s based on a 15th order polynomial fit of the output from the sigma2D function. No value of D yields error >0.1%.