How to create transparent Mat

Question

Am trying to create transparent mat but am getting black background image in return so any idea how to do it as i have to overlay this image with some content on camera video feed.

code i tried.

cv::Mat comp = cv::Mat::zeros( currentImage.size(), CV_8UC4 );
comp.setTo(cv::Scalar(0,0,0,0));
imshow( "transparent", comp );   // show black background image.

Answer 1

thanks to @HansHire and @Scheff we find out that problem is in cv::imshow() it not render transparency so to check Mat for transparency it need to dumped to disk to be checked using system image viewer which render transparency very well

cv::Mat comp = cv::Mat::zeros( currentImage.size(), CV_8UC4 );
comp.setTo(cv::Scalar(0,0,0,0));
// imshow( "transparent", comp );   // show black background image because it cant render transparency .
imwrite( "C:/opencv_dump.png", comp );  // transparent upon opening , thumbnail may look black.