I am making a short clip of tracking and then making 3d object injected in it. I want to make series of png of 3d object then combining my original footage and that 3d object. The problem is when it shows in a rendered pic, it shows checker box which shows transparency but when I see in computer or GIMP (a photoediting tool) it shows black background. I deleted all nodes and made my own by render layer and composer. Changed render layer option to foreground and background both. In background, it shows 3d object with black and in foreground, it shows only black color. Please help me.