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Resolution

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Adrian Quintana edited this page Dec 11, 2017 · 1 revision

resolution_fsc

Purpose

This program allows you to calculate the resolution of one or more volumes or images with respect to a single reference. Three methods are employed:

  • Differential Phase Residual (DPR) In this method the the resolution is defined as the spatial frequency at which the average phase discrepancy between the two transformas exceeds 45 degrees
  • Fourier Ring Correlation (FRC) In this method the resolution is defined as the spatial frequency at which annular samplings of the two Fourier transforms register negligible cross-correlation
  • Spectral Signal-to-Noise Ratio (SSNR) This method is based on the measurement of the signal-to-noise ratio as a function of spatial frequency. The SSNR is determined by comparing the Fourier transform of individual images with that of the global average image. (this option is only available for 2D images not for volumes, see the program ssnr if you are interested in computting the signal to noise ratio in 3D)

The program writes outfilename.dpr andfilename.frc files, for each input volume or image, orselfilename.frc,selfilename.dpr andfilename.snr for theset_of_images mode. These ACSII files contain the DPR, FRC and SSNR as a function of resolution (in 1/Angstrom). The.frc files also contain a column for the FRC expected for pure noise.

Usage


$ resolution_fsc ...

Paramteres

There exist two different modes for this program:

I. Calculate the resolution for images or volumes with respect to a single reference image/volume

  • `` Either a volume or an image file
  • `` Either a volume, an image file, or a selfile containing multiple volumes or images. The input files should have the same (square/cubic) dimensions as the reference file.

I. Calculate the resolution of a set of images, by dividing it randomly in two halves, calculating two average images, and calculate their respective resolution

  • `` Selfile containing the set of images for which to calculate their resolution

Parameters for both modes:

  • `` Sampling rate of the images/volumes, i.e. pixel/voxel size in Angstrom
  • `` Switch off the default to apply the transformation stored in the header of 2D-images

Examples and notes

To calculate "the resolution of a reconstruction", divide the corresponding set of projection images into two subsets (using split_selfile) and reconstruct two volumes from these subsets. This program may then be used to calculate the DPR and FRC between these two volumes. The resulting plots are commonly used to assess the high-resolution limit of the initial reconstruction (see Frank's book for more details).

The syntax would be:


$ resolution_fsc -ref volume_subset1.vol  -i volume_subset2.vol -sam 1

To calculate the resolution of a set of images, the syntax would be:


$ resolution_fsc -set_of_images selfile.sel -sam 1

USER's COMMENTS

--Main.AlfredoSolano - 18 Jan 2007

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