Question

I want to draw a sine wave on a image using openCV. I developed the following code, but the output is not coming as expected:

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include "opencv/cv.h"
#include "opencv/highgui.h"
void main()
{ 
double y[100]; 
      float x; 


  for(x=0;x<100;x++)
  {
      y[(int)floor(x)]=sin(x);

  }

  IplImage *grf = cvCreateImage( cvSize( 200, 200), IPL_DEPTH_8U, 1 );


  for(int x=0;x<100;x++)
  {
  cvLine(grf ,                         /* the dest image */
          cvPoint(x, y[x]),  /* start point */

           cvPoint(x+1, y[x+1]),            /* end point */
           CV_RGB(255, 0, 0),      /* the color; green */
           2, 4, 0);                    /* thickness, line type, shift */

  }


  cvNamedWindow("img", CV_WINDOW_AUTOSIZE);
    cvShowImage("img", grf);
    cvWaitKey(0);
    cvDestroyWindow("img");
    cvReleaseImage(&grf);
}

I have verified the values coming in y array is correct, and plotted these y values using MATLAB. The MATLAB plot is coming a sine wave. Can you tell me why i am not getting correct plot using above code.

My output plot of sine wave is coming as below: you can see I am just getting a horizontal line instead of the sine wave. Any help regarding this?

SOLVED: After following the answer I got the following image:

Thanks

Answer 1

The sin function returns you a value [-1:1], thus you are setting coordinates between line 0 and 1 on your image.
You need to increase amplitude of your sin, shift it’s zero value and reduce a frequency of the sine wave (as sin accepts angle in radians, so you’ll pass a period in 4 steps):

y[(int)floor(x)]=10 + 10*sin(2*.1*PI*x);

So, you will be able to see a sine wave.