Introduction
In the previous version of this tutorial, I showed very simple techniques to composite live action footage with CGI in Blender. Since then, the newer versions of Blender have changed and have made that tutorial useless. The new versions also have added options like RayTracing and better reflections, which will be very useful. In this first part, I'll show how to make a ship fly across the screen and going behind an object in a still image.
Preparations
First, you'll need a picture of something, you can use the picture of my house. Notice that there are no moving parts in the picture, which is very important when using still images. Next you'll need to start Blender, delete the cube and the camera. In front view (Numpad 1), add a new camera and go to the camera view (Numpad 0).
 |
We'll need to see our background image, this is done by pressing View > Background Image, then press Use Background Image and then press the small button next to Image: and browse for myhouse.jpg. You can close the little window. Now you should be able to see the picture in the camera view as well as the 3D view, this will be useful later to setup our cover and shading areas, but if we render the scene, the picture won't get rendered.
There are many ways to have the picture rendered with the scene, some are work well, others don't. But in this tutorial, we'll use the simplest and most effective technique, Backbuff. The only problem with this way is that it doesn't do video, but we'll concentrate on that in the next tutorial.
To setup our Backbuff, go to the Render Buttons, under the Output tab, you should see three rows, the middle one has //backbuff in it, press the little button on the left and choose myhouse.jpg, then press the purple button labeled Backbuff underneath. If you render now, you should see the image rendered.
3D Objects
Now we need to insert a 3D Object, for this tutorial, I'll use the simplest of models, the Romulan BOP. In our scene, press File > Append, choose romulanbop.blend, then choose Object, then press A to select all and press enter. The BOP should be in our scene.
This is the part where you use your own skills, resize the ship, then animate it so that it flies from on end to the scene to the other. You can move the camera to another location, but DON'T animate it.
 |
Cover Areas
Now that the animation is over with, let's add a cover area. As we can see in the image, the ship looks like to goes in front of the middle tree, let's say we wanted to make it go behind the tree. Add a plane, move it in front of the camera, the important thing is that it's facing the camera. In camera view, select the plane and go into edit mode.
Again, use your skills to adjust and move the vertices, make it so that the plane covers the tree. You should end up with something like the image below. I've done it in a very basic way, but obviously for more complex objects, you'll need to make a much better cover area.
 |
Now we'll need to give the plane a special material to make it so it doesn't render, but it does cover the ship when it flies past. There is a simple way to do that, add new material to the plane, then just change A (Alpha) to 0.001. If you render now there's a mask that covers the ship as it flies by.
Well, that covers the first part, as you can see, the results are very effective, the animations looks very good due to the fact that we're using a photo, but it's still not realistic, yet. In the next part, I'll cover lighting, casting shadows and reflections.