After subraction of 4 neighbor pixels always give zero

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I am trying to take difference of center pixel with 4 neighbor and add them and then replace the original with that difference value. but it always replace pixel with zero. I don't what i am doing wrong. thanks for any help

// newproject.cpp : Defines the entry point for the console application.

#include "stdafx.h"
#include "highgui.h"
#include <stdio.h>
#include <cv.h>
#include <highgui.h>
#include <stdio.h>
#include <conio.h>
#include <opencv2/imgproc/imgproc.hpp>  // Gaussian Blur
#include <opencv2/core/core.hpp>        // Basic OpenCV structures (cv::Mat, Scalar)
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include <conio.h>     using namespace cv;
 using namespace std;

  class frameprocessing{

  Mat hsv_base;
  MatND hist_base;

  public:
  void whatever(Mat Frame)
  {
    for(int i=0;i<Frame.cols;i++)
        for(int j=0;j<Frame.rows;j++)
        {
            if(i==0&&j==0)
            {

            //  cout<<"Check 1"<<endl;
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i)-(Frame.at<Vec3b>(j+1,i))+(Frame.at<Vec3b>(j,i)-Frame.at<Vec3b>(j,i+1))+(Frame.at<Vec3b>(j,i)-Frame.at<Vec3b>(j+1,i))+(Frame.at<Vec3b>(j,i)-Frame.at<Vec3b>(j,i+1)));

                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[0]/4;
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[1]/4;
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[2]/4;

            }
            else if(i==Frame.cols-1&&j==Frame.rows-1)
            {
            //  cout<<"Check 2"<<endl;
                Frame.at<Vec3b>(j,i)=((Frame.at<Vec3b>(j-1,i)-Frame.at<Vec3b>(j,i))+(Frame.at<Vec3b>(j,i-1)+Frame.at<Vec3b>(j,i))+(Frame.at<Vec3b>(j-1,i)-Frame.at<Vec3b>(j,i))+(Frame.at<Vec3b>(j,i-1)+Frame.at<Vec3b>(j,i)));
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[0]/4;
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[1]/4;
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[2]/4;
            }
            else if(i==Frame.cols-1&&j==0)
            {
                                      //cout<<"Check 3"<<endl;
                Frame.at<Vec3b>(j,i)=((Frame.at<Vec3b>(j+1,i)-Frame.at<Vec3b>(j,i))+(Frame.at<Vec3b>(j,i-1)+Frame.at<Vec3b>(j,i))+(Frame.at<Vec3b>(j+1,i)-Frame.at<Vec3b>(j,i))+(Frame.at<Vec3b>(j,i-1)+Frame.at<Vec3b>(j,i)));
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[0]/4;
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[1]/4;
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[2]/4;
            }
            else if(i==0&&j==Frame.rows-1)
            {
            //  cout<<"Check 4"<<endl;
                Frame.at<Vec3b>(j,i)=((Frame.at<Vec3b>(j-1,i)-Frame.at<Vec3b>(j,i))+(Frame.at<Vec3b>(j,i+1)+Frame.at<Vec3b>(j,i))+(Frame.at<Vec3b>(j-1,i)-Frame.at<Vec3b>(j,i))+(Frame.at<Vec3b>(j,i+1)+Frame.at<Vec3b>(j,i)));
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[0]/4;
                Frame.at<Vec3b>(j,i)=(Frame.at<Vec3b>(j,i))[1]/4;
                Frame.at ...