title: Create an RGBA image in C++
body: <p>I have a matrix of 640x480x4 values, i.e. 640x480 pixels each with 4 channels (RGBA). I want to create a png file which shows the transparency. I have tried using opencv, but apparently transparency is not supported. What is the quickest and easiest way I can do this, I just need to save a few images?</p>