Bsoft function

Source:

Description:

Algorithm:

	Input: Power spectrum or its logarithm.

	A radial power spectrum is calculated.

	A range of defocus values is tested (100-200000 angstrom, 0.01-20 um), 

	defining the baseline as passing through the zeroes for each defocus 

	and fitting it to a 4th order polynomial.

	The envelope function is a simple gaussian on top of the baseline and

	fitted to minimize the RMSD between the calculated curve and the

	radial power spectrum logarithm.

	The fitting is limited to the spatial frequency range between the 

	first and last zeroes.

	Defocus values are positive for underfocus.

	Functions:

		angle = atan(y/x)

		s2 = reciprocal space distance squared

		defocus_average = (defocus_max + defocus_min)/2

		defocus_deviation = (defocus_max - defocus_min)/2

		defocus = defocus_average + defocus_deviation*cos(2*(angle - astigmatism_angle))

		phase = 0.5*PI*lambda*lambda*lambda*Cs*s2*s2 - PI*lambda*defocus*s2;

		phi_fac = sqrt(1-amp_fac*amp_fac)

		CTF = amp_fac*cos(phase) - phi_fac*sin(phase)

	The new parameters are written into the Bimage structure.

Arguments:

Returns:

Prototype:

Functions used:

Other objects included: