%N cnvlf %F $MIR/src/subs/cnvl.for
%D Convolve the beam with a subimage (the latter being a file).
%P rjs
%: convolution, fft
%B
      subroutine CnvlF(handle,lu,nx,ny,out,flags)

      ptrdiff handle
      integer lu,nx,ny
      character flags*(*)
      real out(*)

  This convolves, or correlates, an image by a beam pattern.  The input
  image is in a Miriad image file. The beam pattern is passed in as a
  handle as previously returned by either the CnvlIniA or CnvlIniF
  routines.

  The output image can either be the same size as the input image (see
  flag='c' below), or the same size as the previously input beam.  In
  the latter case, the output image is centered in the middle of the
  output array.  In particular, if the beam is of size n1 x n2, and the
  input image is of size nx x ny, then the output image will be of size
  n1 x n2, and pixel (i,j) in the input will correspond to pixel
  (x0+i,y0+j) in the output, where
       x0 = n1/2 - nx/2
       y0 = n2/2 - ny/2

  Input:
    handle     Handle of the beam, previously returned by CnvlIniA or
               CnvlIniF.
    lu         Handle of the input Miriad image file.
    nx,ny      Image size.
    flags      Extra processing options:
                'c'    The output is the same size as the input.  The
                       default is the output image is the size of the
                       beam.
                'x'    Correlate with the beam.  The default is to
                       convolve with the beam.
  Output:
    out        The convolved image.
