How to creat and initialized an image with alpha channel in opencv

Question

I have this code, but it doesn't work: (it create an image which is all black)

eqr.create(size,CV_8UC4);
eqr.setTo( cv::Scalar(255,255,255,0)) ;
cv::imwrite("test.png", eqr);

this is also did not work: it creates an image which is all white.

eqr.create(size,CV_8UC4);
eqr.setTo( cv::Scalar(255,255,255,255)) ;
cv::imwrite("test.png", eqr);

What is the correct way to create an image with alpha channel and set all of its pixels to transparent?

Answer 1

You can find similar kind of example here

And if you need load transparent image(with alpha) use

imread("map.jpg",-1)

instead of

imread("map.jpg", CV_LOAD_IMAGE_COLOR)

which will load alpha, See OpenCV Doc for more info.