C++ How to make transparent watermark using OpenCV?

I am trying to make my watermark transparent with low opacity, but it seems just setting the colors to white:

This is the code I'm using which BTW I found in some website

/////////////////// Blending Images (Making Alpha) ////////////////////////    int main()  {      Mat img, img_bgra;      string img_path = "res/test.png";        img = imread(img_path);      if (img.data == NULL)      {          cout << "Image is not loaded!" << endl;          return -1;      }        cvtColor(img, img_bgra, ColorConversionCodes::COLOR_BGR2BGRA);      vector<Mat> channels(4);      split(img_bgra, channels);        channels[3] = channels[3] * 0.1;        merge(channels.data(), 4, img_bgra);        imwrite("res/transparent.png", img_bgra);      imshow("Image", img_bgra);      waitKey(0);      return 0;  }  

I want the watermark to be displayed like this:

How can I achieve that?

https://stackoverflow.com/questions/65871641/c-how-to-make-transparent-watermark-using-opencv January 24, 2021 at 10:16PM