Want transparent image even after blending

Question

I am trying to blend two images as shown here.

This is my whole code

#include 
#include 
#include 

usin         


        

Answer 1

You can blend only pixels that have alpha channel greater than 0, with a custom loop. I think that the code is more clear than an explanation:

#include <opencv2\opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main()
{
    Mat3b bkg = imread("path_to_girl_image");
    Mat4b fgd = imread("path_to_necklace_image", IMREAD_UNCHANGED);

    int x = 150;
    int y = 500;
    double alpha = 0.5; // alpha in [0,1]

    Mat3b roi = bkg(Rect(x, y, fgd.cols, fgd.rows));

    for (int r = 0; r < roi.rows; ++r)
    {
        for (int c = 0; c < roi.cols; ++c)
        {
            const Vec4b& vf = fgd(r,c);
            if (vf[3] > 0) // alpha channel > 0
            {
                // Blending
                Vec3b& vb = roi(r,c);
                vb[0] = alpha * vf[0] + (1 - alpha) * vb[0];
                vb[1] = alpha * vf[1] + (1 - alpha) * vb[1];
                vb[2] = alpha * vf[2] + (1 - alpha) * vb[2];
            }
        }
    }

    imshow("Girl with necklace", bkg);
    waitKey();

    return 0;
}

Result: