FUNCTION	FSHIFT,im0,xsh,ysh

;Fourier shift. Good for sub-pixel shifting: keeps power spectrum unchanged.
;  NOTE: don't use on non-square or odd-sided images.
;Create AHB 08/01
;Removed total flux normalization.  Photometry now preserved, but note that
;  negative values are cut off. AHB 03/04

  if not KEYWORD_SET(int) then int = 0

  sz = (SIZE(im0))(1)
  u = [FINDGEN(sz/2),FINDGEN(sz/2)-(sz/2)]
  v = [[FINDGEN(1,sz/2)],[FINDGEN(1,sz/2)-(sz/2)]]
  uu = REBIN(u,sz,sz)
  vv = REBIN(v,sz,sz)
  k = COMPLEX(0, (-2) * !pi * (uu*xsh + vv*ysh) / sz)
  ;im1 = ABS(FFT(FFT(im0) * EXP(k), /inverse))
  im1 = FLOAT(FFT(FFT(im0) * EXP(k), /inverse))

RETURN,im1
END