No window to render

Hello, everyone. I have a question needed your help!
I want to input a 2D image and fuse the results of 2D image processing with 3D model. The output is pixel of this fused result that will become input of other function. And I don’t need to open any window.
I wonder if I can render without starting the engine of Urho3D and opening any window. I search the headless mode, but it seems that this mode can not render.
So I want to ask if there is any possible solution to this problem. Thank you very much~