TF ED - Transfer Function - Estimation of CTF parameters

PURPOSE

Estimates the defocus, astigmatism, and cutoff frequency of high frequencies based on 2-D power spectrum.

USAGE

.OPERATION: TF ED, [ang],[mag],[astdef],[overdef],[cutoff]

[On output, [ang], [mag] are the angle and magnitude of astigmatism. [astdef] is the astigmatism corrected defocus value. [overdef] is the overall defocus without taking astigmatism into account. [cutoff] is the cutoff frequency in 1/A]

INPUT FILE: PW_AV001 [Enter the name of the 2-D power spectrum file.]

.PIXEL SIZE [A], SPHERICAL ABBERATION CS [MM]: 2.8, 2

.WAVELENGTH LAMBDA(ANGSTROMS): 0.037
[Enter the wavelength of the electrons. The value used in this example corresponds to 100kV. A table of values is listed in the glossary under lambda.]

.AMPL. CONTRAST RATIO [0-1]: 0.1

.OUTPUT DOCUMENT FILE: CTF001

NOTES

1. The output document file contains the following four columns: a). - Spatial freqency (1/A). b). - The estimated background noise: BACKGROUND_NOISE(f)**2. c). - The background-subtracted power spectrum: {CTF(f)*ENV(f)*SIGNAL(f)}**2=PW(f)-BACKGROUND_NOISE(f)**2 d). - The estimated ENV(f)**2

2. The model of the power spectrum is: PW(f) = {CTF(f)*ENV(f)*SIGNAL(f)}**2+ BACKGROUND_NOISE(f)**2

3. For details about this algorithm and cutoff frequency see: Z. Huang, P.R. Baldwin, and P. A. Penczek. Automated determination of parameters describing power spectra of micrograph images in electron microscopy. (J. Struct. Biology 144,2003,79-94 )

4. In case of the power spectrum has quite weak CTF imprint, the operation will not give atigmatism estimation, and only will give an estimation of the overall defocus and the cutoff frequency.

5. The amplitude contrast is set by default to 0.1.

6. Implemented by Zhong Huang.

SUBROUTINES

TFED, GETDEFOCUS, CL1, LSFIT

CALLER

UTIL1