Bsoft function

img_ctf_apply

Source:

src/img/img_ctf.c

Description:

Applies or corrects for the contrast transfer function (CTF).

Algorithm: 

	The actions for this funtion are:

	1	flip phase (multiply by the sign of the CTF)

	2	apply a CTF (multiply with the CTF)

	3	correct for the CTF: ctf/(ctf^2 + wiener_factor)

	4	correct for the CTF: env*ctf/((env*ctf)^2 + noise^2)

	5	correct for the CTF with baseline: ctf/(ctf^2*noise^2 + wiener_factor)

	6	correct for the CTF with baseline: 1/(ctf*noise + sign*wiener_factor)

	Functions:

		angle = atan(y/x)

		s2 = x*x + y*y

		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)

	Note: Defocus is positive for underfocus and negative for overfocus.

	All of the parameters required to calculate the CTF, envelope and baseline

	functions are embedded in the CTF structure.

Arguments:

Bimage* pimage (modified).
CTF* em_ctfCTF parameter structure.
float wienerWiener factor (fraction).
int actionaction to be taken.
float loreslow resolution limit.
float hireshigh resolution limit.

Returns:

int 0, <0 on error.

Prototype:

int img_ctf_apply(Bimage* p, CTF* em_ctf, float wiener, int action, float lores, float hires)

Functions used:

bfree
check_defocus_and_Cs
ctf_baseline_calculate
ctf_envelope_calculate
electron_wavelength
generate_baseline_equation
generate_envelope_equation
img_fft

Other objects included:

struct Bimage
struct Bmarker
class Complex
constant M_PI

Generated by bdoc.pl on Mon Jun 15 11:47:47 2009

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