OpenCV Create Transparent Background

 In this post I am showing how the background of an image replaced with transparent background. Here the background is black color. The procedure includes the following.

Load and Convert color image to gray scale

    Mat src=imread("source.jpg",1);
    Mat dst,tmp,alpha;
    cvtColor(src,tmp,COLOR_BGR2GRAY);

Threshold the image to create alpha mask.

    threshold(tmp,alpha,50,255,THRESH_BINARY);

Split source image to separate RGB channel

    Mat rgb[3];
    split(src,rgb);

Now merge RGB channel and alpha to create new image

    Mat rgba[4]={rgb[0],rgb[1],rgb[2],alpha};
    merge(rgba,4,dst);
    imwrite("dst.png",dst);

Full Code

    Mat src=imread("img/1.jpg",1);
    Mat dst,tmp,alpha;

    cvtColor(src,tmp,COLOR_BGR2GRAY);
    threshold(tmp,alpha,50,255,THRESH_BINARY);
    imwrite("alpha.jpg",alpha);

    Mat rgb[3];
    split(src,rgb);

    Mat rgba[4]={rgb[0],rgb[1],rgb[2],alpha};
    merge(rgba,4,dst);
    imwrite("dst.png",dst);