NAME

     Butterworth_High - performs Butterworth highpass filtering

SYNOPSIS

      #include <math.h>
      #include <stdio.h>
      #include <stdlib.h>
      #include "CVIPdef.h"
      #include "CVIPimage.h"

     Image *Butterworth_High(Image *in_Image, int block_size, int
     dc, int cutoff, int order)

      <in_Image> - pointer to an Image structure
      <block_size> - desired block size
      <dc> - drop(0) or retain(1) dc component
      <cutoff> - cutoff frequency
      <order> - filter order

PATH

     $CVIPHOME/XFORMFILTER/filter.c

DESCRIPTION

     Butterworth_High()  performs   two-dimensional   butterworth
     highpass  filtering in transform domain on input image.  The
     parameter cutoff defines  the  cut-off  frequency  locus  at
     points  for  which the filter transfer function H(u,v) is at
     0.7071 of its maximum value. All components inside the  cir-
     cle (or 1/4 circle if dc component is on the upper-left-hand
     corner of  its  transform  plane)  of  radius  "cutoff"  are
     attenuated  according  to  the  transition  from passband to
     stopband, depending on the degree of filter  order  f_order.
     All  frequencies   component outside the circle (or 1/4 cir-
     cle) are passed with no attenuation.   If dc equals  1,  the
     dc   component  will  be  retained, if dc = 0, dc componenet
     will be dropped.

TYPES AND CONSTANTS

     None

RETURN VALUES

     A filtered image

HISTORY

     History information recorded: None

DIAGNOSTICS

      The Butterworth_High filter will work for both  real-valued
     and  imaginary-  valued  transform.  If  the  origin  of the
     transform is on the center of its frequency plane (shifted),
     the cutoff frequency can range from 1 to blocksize/2 and the
     Butterworth_High  function  can  be  called  directly   with
     correct   parameters.  If  the origin of the transform is on
     the  upper  left-hand  corner  of   its   frequency   plane,
     nonfft_xformfilter() must be used to call Butterworth_High()
     with filtertype=4. The cutoff frequency in   this  case  can
     range  from  1  to  blocksize  since a block is treated as a
     quarter of a regular block with its origin on the center. If
     hpf_setup()  is  to  be used to call Butterworth_High(), the
     transform must be setup and recognized by hpf_setup(),  oth-
     erwise   the   setup   program   automatically  assumes  the
     transform's dc component is on the center (dcpos=1).

EXAMPLE

      #include <CVIPtoolkit.h>
      #include <CVIPimage.h>
      #include <CVIPdef.h>
      #include <CVIPconvert.h>
      #include <CVIPview.h>
      #define VIEWER "picture"
      #define VIDEO_APP "SunVideo &"

      void main()
      {
      Image *cvipImage;
      IMAGE_FORMAT format;
      char *inputfile,*outputfile;

      (void) setDisplay_Image(VIEWER, "Default");
      print_CVIP("\n\t\tEnter the  Input File Name:  ");
      inputfile =(char *) getString_CVIP();
      format = getFormat_CVIP(inputfile);
      cvipImage = read_Image(inputfile,1);
      view_Image(cvipImage, inputfile);
      free(inputfile);
      /* the following call performs the fft_transform on
      the input image with the block size equal to 256 */
      cvipImage=(Image *)fft_transform(cvipImage,256);
      /* the following call performs the butterworth high
      pass filtering of order 2 on the transformed image with
      the cut off frequency equal to 64 */
      cvipImage = (Image *)Butterworth_High(cvipImage,256,
      1,64,2);
      /* the following call performs the inverse fft_transform
      in the filtered image with the block size equal
      to 256 */
      cvipImage = (Image *)ifft_transform(cvipImage,256);
      print_CVIP("\n\t\tEnter the Output File Name:  ");
      outputfile = getString_CVIP();
      view_Image(cvipImage,outputfile);
      write_Image(cvipImage,outputfile,CVIP_NO,CVIP_NO,format,1);
      free(outputfile);
      }

SEE ALSO

     libxformfilter

AUTHOR

     Copyright (C) 1996 SIUE - by Scott E. Umbaugh and Simon Low.