How Do I Performs Two Gaussian Smoothings (Of Two Different Sizes By Product Of 1.6) On The Image, Then Get The Weighted Difference Between The Two By Using Opencv In Vc++

#include <opencv\cv.h>
#include <opencv\highgui.h>
using namespace cv;

void smooth( IplImage* image)
{
	IplImage* out = cvCreateImage( cvGetSize(image), IPL_DEPTH_8U, 3 );
	cvSmooth( image, out, CV_GAUSSIAN, 15, 15 );
	cvShowImage( "out", out );
	cvReleaseImage( &out );
}

int main( int argc, char** argv )
{
	
	IplImage * img;
	img = cvLoadImage("a.jpg");
	cvShowImage("second", img);
	smooth( img );

	cvWaitKey();

	cvDestroyWindow("second");
	cvReleaseImage(&img);

	return 0;
}