Digital Video Compositing in Blender

A tutorial explaing how to use uncompressed video as an animated texture which can be applied to a plane (or any object) and used for compositing with Blender 3D graphics

Working with objects in Blender is very fast and intuative once you get to know the techniques. Being able to manipulate a 'plane' to which you have applied full motion video is a bit like positioning a screen behind your foreground detail in real life. If you also cut and shape your background plane to suit the foreground graphics, you have great potential for video compositing and special effects. There are other, more acurate methods of combining live video with animated 3D objects but if you don't need pixel level accuracy, this method is quick, simple and effective. Right, let's get on with it then.

1. Preparing your background video clip

Blender can use uncompressed AVI video files as animated textures so the first thing to do is to make sure your background video is in the right format. I use Adobe Premiere to grab video from my Canon DV camcorder and then export the clip as an uncompressed AVI file. Any decent DV NLE package should allow you to export as Uncompressed AVI.

In Premiere, import the clip and drag it to the timeline. Then highlight the clip and choose 'Export Clip', 'Movie' from the file menu.

From the Export Movie dialogue choose 'Settings'

From the Export Movie Settings dialogue you must choose Microsoft AVI as the file type (not Microsoft DV AVI).

Fig 1. Choosing the file type

Now change from 'General' to 'Video' from the Settings list and from the Compressor list choose 'None'. This is important as Blender will complain about unsupported file formats if you don't do this!

Fig 2. Choosing 'Compressor', 'None' from the list

Having adjusted your export settings, make a final check that the Compression is 'None' @ 100% and go ahead and save to a file.

Fig 3. Saving the Uncompressed file

2. Adding the video to a plane in Blender

Right, now the fun begins. Fire up Blender and add a simple plane. This represents a 'projection screen' in front of which you can place your 3D objects. Just like setting up a 'real' rear-projection stage!

Fig 4. The plane used as a 'projection screen'

With the plane selected. add a new material (hit F5) and to this material add a new texture (hit F6). Now in the Texture Settings you need to make a few choices. 1. Select 'Movie' as the texture type. 2. Use the 'Load Image' button to browse to your saved uncompressed AVI file. 3. Set the total number of frames in the video clip (this will already be shown at 4.) 5. Set the length of the clip, again in frames. My example clip has only 42 frames but yours may have many more (at 25 frames per second of screen time.)

Fig 5. The texture button settings for your video clip texture

Back in the Material settings (F5) you need to give the material an Emit value of 1. This is to make the image 'project' from the 'screen' by emitting light from itself.

Fig 6. The material has an 'Emit' value of 1

Additional Material settings are as shown in Fig 7 below. These are all the defaults so no need to change anything (except one important option, the 'Shadeless' button. This is not selected yet but we will come back to this in a moment when we put some 3D objects in our scene.)

Fig 7. Other material settings

3. Positioning the 'screen' and rendering

Right, now position your camera to point at the plane in your scene and hit F12 for a render. Here I have intentionally pulled the camera back and set it at an angle from the plane so you can see that the video clip really is attached to the plane as a texture. I could move or reshape the plane anyway I wanted now and the video would remain intact on the 'screen'.

Fig 8. The plane is rendered with the video, just like a rear projection screen

Now, to use this setup as a simple background screen, just like rear projection, you should position your camera so that it is pointing straight at the background plane. You will also want to adjust the distance between the camera and the plane so that it extends just beyond the outer safe area in the viewfinder, as shown in Fig 9. (check this by looking at the camera view, hit key 0 on the Num Pad.)

Fig 9. The background plane fills the viewfinder

So now you have your background video plane in position. Since you will no doubt want to combine some foreground graphics with this background footage, you can now position and animate your 3D Blender objects in front of the 'screen'. These 3D objects will need lighting so go ahead and position some lights too. Now, to avoid the foreground lighting 'washing out' the background video on the screen, select the plane and in its' material settings make sure you click the 'Shadeless' button. This will prevent the foreground lights having any effect on the background footage.

Fig 10. Click the 'Shadeless' button to prevent the foreground lighting washing out the video footage

4. The final composite

So now, all you have to do is set your render preferences and render the whole stage to an AVI file. As your foreground objects animate, so the background video (as an animated texture) automatically advances each frame. Your foreground objects can move towards and away from (and even embed themselves in) your background 'screen'. There is no need for any Alpha Channel or Blue Screen type keying effects. The background footage is just another object with material and texture attribute and so is rendered along with all you other objects perfectly. and in sync with your animation.

Fig 11. Foreground objects and background footage rendered together perfectly.

That's it. The beauty of this technique is that you don't need to take your animations and background footage into a package like Adobe After Effects in order to combine them.

Using the 'World' environment to add a video background

If you want your background video to exactly match your camera viewpoint without having to position your background plane then use the following technique.

The World environment can use an animated texture too, but it has to ba a texture which is already attached to an object. Add the video clip as a texture to any object (a simple plane for instance), give the object a name and position the object somewhere 'off camera'.

Then go to the 'World' buttons screen and add a New World.

Choose 'Paper' as the World Background type. In the Texture section, click the 'View' button and in the box above the view button, type the name of the object you just gave your animated texture to.

Click the 'Hori' button.

From the texture browse button, choose the animated texture you attached to your 'off-screen' object.

If all is well, you should see the first frame of your video clip texture in the preview window to the left of the World buttons (see Fig 12.)

Fig 12. Choose 'Paper' as the World type

Fig 13. Choose the object with the texture (Plane) and choose the texture itself (BGVideo)

Now when you render your animation the background video appears magically behind your scene perfectly matched in terms of size and aspect ratio.

Also remeber that you can place a single frame of your video (create one in Premiere before you start) as a window background to help you model your objects in relation to your background video footage (rotoscoping as it is called in the film industry, from the technique of projecting a single frame of your background plate onto animation paper so you can draw precisely over it to match movements etc.)

Conclusion

So that's it for this tutorial. Hope that seems clear. Once you've rendered your animation you can then import it back into Premiere (or the editing package of your choice) for inclusion in your latest epic! Good luck.

If you have any comments about this technique then please make them in the Discussion Forum. At some point I might setup 'comments posting' facility for each and every tutorial I create but for now, please use the Forum.

Happy Blending,

Rob Coldwell.

Blender Discussion Forum

Take the time to visit the Blender discussion forum where you can hopefully exchange tips and get advice from fellow Blender users.

Meanwhile, download Blender for Windows or Blender for Linux and get Blending!

NB, the above binaries downloads will remain available until such time as Blender.org release binaries themselves. At that time I will remove the above files. Source code however, is available for download now at Blender.org

[ Blender Web Ring Home]
[Prev] [Random] [List All] [Next]

 Home | 3D Graphics | Gallery | Perl | Film Making

Site hosting by UKShells

Copyright 2006 Rob Coldwell - To feedback to upperfold: click here

Visit YourArtShop for quality prints of original paintings