## NAME

         rayleigh_noise - Add Rayleigh noise to an image

## SYNOPSIS

         #include "CVIPnoise.h"

         Image *rayleigh_noise(Image* imageP,float *variance);

          <imageP> - pointer to Image structure
          <var> - variance of noise distribution

## PATH

         $CVIPHOME/NOISE/noise.c

## DESCRIPTION

         Rayleigh type noise appears typically  in  radar  range  and
         velocity  images  and  is derivable from uniform noise.  The
         Rayleigh noise histogram is defined as:

                     Gi
              hi = --------exp(-Gi^2/(2a^2) 0<=Gi<infinity
                     a^2

         where Gi is the grey-level value of the ith pixel,  and  the
         mean can be defined as follows: mean=sqrt(pi/2a).

## RETURN VALUES

         The rayleigh_noise() function  returns  the  modified  Image
         pointer on success, and returns a NULL pointer on failure

## BUGS

         none

## EXAMPLE

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

          void main()
          {
          Image *cvipImage;
          IMAGE_FORMAT format;
          char *inputfile,*outputfile;
          float var=100.0;
          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 adds rayleigh noise to the input
          image with the variance equal to 100.0.We can use the
          function rayleigh_noise_setup so that the user can
          specify the inputs  */
          cvipImage = rayleigh_noise(cvipImage,&var);
          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

         gamma_noise(3),     gaussian_noise(3),     neg_exp_noise(3),
         speckle_noise(3), uniform_noise(3)

## AUTHOR

         Copyright (C) 1992, 1996 SIUE -  by  Scott  E.  Umbaugh  and
         David Lyons.