why is it so slow for my background subtraction

// Background subtraction with edge detection.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <cv.h>
#include <cvaux.h> 
#include <highgui.h> 
#include <ctype.h> 
#include <stdio.h> 
 
IplImage *frame1 = NULL, *frame2 = NULL, *frame3 = NULL; 
IplImage *diff1 = NULL, *diff2 = NULL, *result = NULL; 
//IplImage* cannyImg; 
IplImage *grayImg = 0; // gray image 
 
int main(int argc, char** argv) 
{ 
int height,width,step,channels; 
uchar *data1, *data2, *data3, *diffData1, *diffData2, *resultData; 
 
int i, j; 
int threshold = 30; 
int diff; 
 
/* Start capturing */ 
 
 
CvCapture* capture = cvCaptureFromCAM( CV_CAP_ANY );
	if( !capture ) 
	{
    fprintf( stderr, "ERROR: capture is NULL \n" );
    getchar();
    return -1;
	}
	
 
//capture = cvCaptureFromAVI("C:\Documents and Settings\biob202\Desktop\ax fyp\optical_flow_input.avi"); 
 
 
int //mode = CV_RETR_EXTERNAL; 
  
    mode = CV_RETR_EXTERNAL; //detect both outside and inside contour 
  
 
if( !capture ) 
 
{ 
        
fprintf(stderr,"Could not initialize...\n"); 
//return -1; 
 
} 
 
/* Capture 1 video frame for initialization */ 
 
frame2 = cvQueryFrame(capture);    // retrive from the video 
frame3 = cvQueryFrame(capture); 
 
/* Create windows */ 
 
cvNamedWindow("Actual Video", 1);    // creating window 
 
cvNamedWindow("With Differencing", 1); 
cvMoveWindow("With Differencing", 500,0); 
cvNamedWindow("BackGround", 1); 
cvMoveWindow("BackGround", 100,350); 
 
//cvNamedWindow("canny Edge",1); 
//cvMoveWindow("canny Edge", 750, 350); 
 
CvBGStatModel* bg_model; 
 
bg_model =cvCreateGaussianBGModel( frame2 ); 
 
 
/* Get properties of frame */ 
width = frame2->width; 
height = frame2->height; 
step = frame2->widthStep; 
channels = frame2->nChannels; 
 
int key=-1; 
while(key != 'q') 
{ 
        
 
/* Get consecutive frames */ 
frame1 = cvCloneImage(frame2); 
 
// cvReleaseData(frame2); 
// cvReleaseImage(&frame2); 
frame2 = cvCloneImage(frame3); 
 
// cvReleaseData(frame3); 
// cvReleaseImage(&frame3);  
frame3 = cvQueryFrame(capture); 
 
/* Initialize difference and result frames */ 
diff1 = cvCloneImage(frame3); 
diff2 = cvCloneImage(frame3); 
result = cvCloneImage(frame3); 
 
 
/* Image is treated as at unsigned char data hence we use an 
unsigned char pointer to point to the same to access pixels */ 
 
data1 = (uchar *)frame1->imageData; 
data2 = (uchar *)frame2->imageData; 
data3 = (uchar *)frame2->imageData; 
diffData1 = (uchar *)diff1->imageData; 
diffData2 = (uchar *)diff2->imageData; 
resultData = (uchar *)result->imageData; 
 
 
/* Get difference of frames */ 
cvAbsDiff(frame2,frame1,diff1); 
cvAbsDiff(frame3,frame2,diff2); 
cvUpdateBGStatModel( frame2, bg_model ); 
 
 
 
// Check for threshold 
 
for(i=0;i<=height-1;i++) 
{ 
for(j=0;j<=width-1;j++) 
{ 
//Difference depends on sum of pixels on each channel 
 
if(((diffData1[i*step+j*channels+0] + 
diffData1[i*step+j*channels+1] + diffData1[i*step+j*channels+2]) > 
threshold) && ((diffData2[i*step+j*channels+0] + 
diffData2[i*step+j*channels+1] + diffData2[i*step+j*channels+2]) > 
threshold)) 
{ 
resultData[i*step+j*channels+0] = 255; 
resultData[i*step+j*channels+1] = 255; 
resultData[i*step+j*channels+2] = 255; 
} 
else 
{ 
resultData[i*step+j*channels+0] = 0; 
resultData[i*step+j*channels+1] = 0; 
resultData[i*step+j*channels+2] = 0; 
} 
} 
}
 
//end of frame differencing with binarization 
 
grayImg = cvCreateImage( cvSize(result->width, result->height), 
IPL_DEPTH_8U, 1 ); 
    
    //convert original color image (3 channel rgb color image) to gray-level image 
    cvCvtColor( result, grayImg, CV_BGR2GRAY ); 
   // cannyImg = cvCreateImage(cvGetSize(result), IPL_DEPTH_8U, 1); 
 
// cvCanny(grayImg, cannyImg, 50, 150, 3); 
 
 
cvShowImage("Actual Video",frame2); 
cvShowImage("With Differencing",result); 
cvShowImage("BackGround", bg_model->background); 
//cvShowImage("canny Edge", cannyImg); 
 
  
 
cvReleaseImage(&frame1); 
cvReleaseImage(&diff1);  
cvReleaseImage(&diff2); 
cvReleaseImage(&result); 
 
key = cvWaitKey(10); 
}//end of while 
 
 
cvDestroyWindow("Actual Video"); 
cvDestroyWindow("With Differencing"); 
cvDestroyWindow("BackGround"); 
//cvDestroyWindow("canny"); 
cvReleaseCapture(&capture); 
 
return 0; 
}