**PURPOSE**- Applies Fourier filter to 2D or 3D, real or Fourier image. Coefficients of the filter are read from first register column of a document file. Example.

**SEE ALSO****FD C**[Fourier filter image/volume according to specifed column of Document file ||] **FF**[Filter - Fourier]

**USAGE**- .OPERATION: FD

- .INPUT FILE: IMG001

[Enter name of input file.].OUTPUT FILE: IMG002

[Enter name of output file.].FILTER DOC FILE: my_filter

[Enter name of document file. First column should contain coefficients of a Fourier filter.]

**NOTES**

- The Fourier transform of the input file is multiplied
by the filter coefficients read from a document file.
Filter coefficients should be stored in in the first
column. The first key is assumed to correspond to zero
frequency, the second key to the first bin in Fourier
space, and so on. If the document file has fewer keys
than the number of bins in Fourier space (SQRT(2)*[N/2+1],
where N is the maximum dimension of the image in real space),
the remaining filter coefficients are assumed to be equal
to zero. Real input image will have real output and a Fourier
input will have a Fourier output.
- Implemented by P. Penczek.

**SUBROUTINES**- FILTDOC

**CALLER**- FOUR1

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