BP R2 - Back Projection - Weight image series ||

PURPOSE

Apply R**2 or R* weighting to the series of 2D projections using built-in Parzen filter function. Applicable to the evenly distributed 2D projections or in the cases when large number of randomly distributed projections approximates an even distribution. Provides quick and efficient way to obtain 3D reconstruction (in particular in conjunction with 'BP RP' operation with one iteration step specified). For more accurate 3D reconstruction either general weighting ('BP 3D') or iterative reconstruction ('BP RP') has to be used. The dimensions of projections do not have to be powers of two. See: Comparison of 'BP' operations.   Example.

SEE ALSO

BP 3D	[Back Projection - 3D, using Euler angles ||]
BP CG	[Back Projection - 3D, Iterative, Conjugate Gradients ||*]
BP RP	[Back Projection - 3D, iterative, Richardson, constrained ||*]
BP S2	[Back Projection - 2D, single tilt, iterative, constrained ||]
BP W2	[Back Projection - 2D, filtered, weighted ||]

USAGE

.OPERATION: BP R2

.TEMPLATE FOR 2-D IMAGES: PRO***
[Enter the prefix of the projection file series.]

.TEMPLATE FOR 2-D OUTPUT FILES: PRW***
[Enter the prefix of the weighted projection file series.]

.SELECTION DOC FILE: SEL_SERIES_001
[Enter selection document file name containing the numbers of the input images in the first register column.]

.CUT-OFF FREQUENCY FOR PARZEN FILTER: 0.25
[For cut-off equal zero, R**2 weighting and no filter is applied.
For cut-off larger than zero, R**2 weighting and Parzen filter is applied.
For cut-off equal -1.0, R* weighting and no filter is applied.
For cut-off smaller than zero, R* weighting and Parzen filter (with positive cut-off) is applied.]

NOTES

1. R**2 (squared R) weighting is appropriate for 3D reconstruction.

2. R* (R-star) weighting is appropriate for 2D reconstruction.

3. During weighting the images are padded with the average to double the size.

4. Implemented by: Paul Penczek.

SUBROUTINES

BPWR, BPWR_Q

CALLER

VTIL2