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BP GW3D - General Weighting function in 3D

(MR 9/17/94)

PURPOSE

Calculate a three-dimensional weighting function or transfer function for application to a three-dimensional reconstruction obtained by simple backprojection. Optionally apply the weighting function to a three-dimensional Fourier transform. More details about the theory can be found in the manual for BP GW. Arbitrary Geometry.

SEE ALSO

BP 3 [(ART Back Projection - 3D)]
BP 3D [(3D Reconstruction - using three Eulerian angles)]
BP 3E [Back Projection in X-Y planes]
BP GW [3D reconstruction with general weighting]
BP LOCAL [Back projection calculated to a specific local area]
BP MEM2 [2D reconstruction by Max. Entropy Method]
BP RP [Iterative Reconstruction With Constraints]
BP R2 [R**2 weighting for 2D]
BP S2 [2D Single-tilt Iterative Recon. With Constraints]
BP W2 [2D filtered weighted Back Projection]
BP WX [Weighted Back Projection]
BP WY [Weighted Back Projection]
BP XY [Back Projection in X-Y planes]

USAGE

.OPERATION: BP GW3D

.(S)INC-FCT. OR (G)AUSS-FCT.: S
[Enter S if the weighting function is to be calculated by a superposition of sinc-functions, G if it is to be calculated as a superposition pf Gaussian functions. Sinc function can through numerical inaccuracies lead to fringes in the reconstruction if the sampling is very uneven. As Gauss-functions are smoother they do not create these fringes, however, they correspond to an appodization of the backprojected rays in real space by using a Gaussian envelope function instead of a step function.]

.(W)EIGHTING- OR (T)RANSFER-FUNCTION: W
[Enter W if you want to calculate the weighting function, T if you want to calculate the transferfunction of the back-projection.]

If W was answered:

.CRITICAL VALUE FOR W: 0.6
[Enter a threshold level for the weighting function. I.e. every value in the weighting function that is below the "critical value" is replace by it.]

.3D VOLUME DIAMETER: 64.0
[Enter the ray lenght for the simple backprojection. This is the width of the step function or the halfwidth of the Gaussian function that limits the back-projection ray in real space.]

.GENER.ANGLES IN (L)ABEL,(D)OCF,(E)XTERNAL: L
[Angles of the projections can be provided in the header (L)abel of the projection files or by a document file or external.]

.FILE NUMBERS OF PROJECTION FILES: 1-5

.TEMPLATE OF PROJECTION FILE SERIES: PRN001

.INPUT FILE: volume001
[You can enter the name of a Fourier transform of a volume to which the weighting function is then applied. This file needs to be in the simple format 3D Fourier format (see CP SF3). If the answer is "*" then the function will only be calculated but not applied.]

.WEIGHT FILE: weight001
[Enter name for 3D weighting function]

If no input 3D file was given, then the program needs to know the dimensions:

.NSAM,NROW: 66 64

.NSLICE: 64
[Note that the function also will be stored in sinple 3D Fourier format. NSAM needs to be 2 point larger than the real space value.]

SUBROUTINES

GENW3D

CALLER

VTIL2

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