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Let me answer my own question from knowledge of others and other visitors ease . The answer i got from here by @Andrey Somorodov , below program will give you your required result and requirement

#include <iostream>
#include <vector>
#include <stdio.h>
#include <functional>
#include <algorithm>
#include <numeric>
#include <cstddef>
#include "opencv2/opencv.hpp"
#include <iostream>
#include <fstream>

using namespace std;
using namespace cv;
 int main( int argc, char** argv )
{
    namedWindow("Image");

    Mat Img1=imread("Img1.png",-1);
    Mat Img2=imread("Img2.png");
    cv::resize(Img1,Img1,Img2.size());
    Img1.convertTo(Img1,CV_32FC4,1.0/255.0);
    Img2.convertTo(Img2,CV_32FC3,1.0/255.0);

    vector<Mat> ch; 
    split(Img1,ch);

    Mat mask = ch[3].clone();              // here's the vignette

    ch.resize(3);

    Mat I1,I2,result;

    cv::multiply(mask,ch[0],ch[0]);
    cv::multiply(mask,ch[1],ch[1]);
    cv::multiply(mask,ch[2],ch[2]);
    merge(ch,I1);

    vector<Mat> ch2(3);
    split(Img2,ch2);
    cv::multiply(1.0-mask,ch2[0],ch2[0]);
    cv::multiply(1.0-mask,ch2[1],ch2[1]);
    cv::multiply(1.0-mask,ch2[2],ch2[2]);
    merge(ch2,I2);

    result=I1+I2;

    imshow("Image",result);
    waitKey(0);
}