## NAME

         High_Freq_Emphasis  -  performs  high   frequency   emphasis
         filtering

## SYNOPSIS

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

         Image *High_Freq_Emphasis(Image *in_Image,int block_size,int
         dc,int Cutoff,float alfa,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
          <alfa> - a constant (typically 1.0 to 2.0)
          <order> - filter order

## PATH

         $CVIPHOME/XFORMFILTER/filter.c

## DESCRIPTION

         High_Freq_Emphasis() performs a  two-dimensional  high  fre-
         quency  emphasis  filtering  in  transform  domain  on input
         image.It is implemented by adding a constant  to  a  butter-
         worth high pass filter transfer function. This preserves the
         low frequency components of the image and at the same  time,
         amplifies  the high-frequency components. The result of this
         process is better tonality in the final image.  The  cut-off
         frequency cutoff and filter order <order> is for the butter-
         worth high pass filter used in this high frequency  emphasis
         filter.  Experiment  revealed  that the constant alfa in the
         range of 1.0 to 2.0 yields good result. If dc equals 1,  the
         dc  component  will be retained, if it equals 0, the dc com-
         penent will be dropped.

## TYPES AND CONSTANTS

         None

## RETURN VALUES

         A filtered image

## HISTORY

         History information recorded: None

## 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 high frequency emphasis
          on the transformed image with the cut off frequency equal
          to 64 and alpha equal to 1.2 */
          cvipImage = (Image *)High_Freq_Emphasis(cvipImage,256,1,
          64,1.2,2);
          /* 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.