## NAME

         neg_exp_noise - Add Negative Exponential noise to an image

## SYNOPSIS

         #include "CVIPnoise.h"

         Image *neg_exp_noise(Image *imageP,float *var);

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

## PATH

         $CVIPHOME/NOISE/noise.c

## DESCRIPTION

         Negative Exponential type noise is the result  of  acquiring
         an image illuminated with a coherent laser.  The optics com-
         munity refers to this type of noise as laser speckle. It has
         a histogram as indicated by the following equation:

                     1
              hi = ----exp(-Gi/a)
                     a

         where Gi is the grey-level value of the ith  pixel,  a*a  is
         the variance.

## RETURN VALUES

         The neg_exp_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 negative exponential noise
          to the input image with the variance equal to 100.0.
          We can use the function neg_exp_noise_setup so
          that the user can specify the inputs  */
          cvipImage = neg_exp_noise(cvipImage,&var);
          print_CVIP("\n\t\tEnter the Output File Name:  ");
          outputfile = getString_CVIP();
          view_Image(cvipImage,outputfile);
          free(outputfile);;
          }

## SEE ALSO

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

## AUTHOR

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