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

**USAGE**- .OPERATION: FD C

- .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 contains coefficients for a Fourier filte.].DOC REGISTER NUMBER: 2

[ Register column in doc file which contains coefficients for the desired Fourier filter.]

**NOTES**

- The Fourier transform of the input file is multiplied
by the filter coefficients read from a document file.
The first key from the doc file 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. A real input image will have real output and Fourier input will have a Fourier output. - Implemented by P. Penczek.

**SUBROUTINES**- FILTDOC

**CALLER**- FOUR1

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