View Full Version : how do you mix reality Video with LW

Mr Rios
03-27-2003, 03:22 AM
I was wondering whether anyone could help he with a query, that is... how do you mix a lightwave 3d rendered AVI video with real video? For example how did the makers of jurassic park digitally combine the T-rex with the actors and props.

I've tried serveral techniques, such as animating a model behind a blue "Backdrop," and making the blue transparent in Adobe Premier. But it doesn't give a realistic effect, especially due to the fact that the objects can't have shadows.

If anyone out there knows of how to do this, or you are someone that has worked on films that have done such Visual effects, then please could you reply to this question. Or even suggest other addon software that is capable of it.



03-27-2003, 04:14 AM
Well, one way (there are several) is to use your real footage as a backdrop, if its something simple like a flat area of ground u would make a large plane and position it (and move the camera) so the plane matches up with the ground in the backdrop, then apply Front Projection Mapping to the plane (in surface editor hit the T next to colour and select "Front" as the mapping type for Image and select the backdrop image as the image map) what this will do is basically hide the plane, it will just look like the backdrop, but it will recive shadows, making it look like your 3d objects are casting shadows on the floor in the real video footage.


03-27-2003, 04:24 AM
Heres a quick example using an image of the view from my bedroom window :)

note i havn't matched the shadows up, what ud want to do is get the shadows cast from your objects to match as close as posible to the shadows in the image, on here if u look at the fence posts the shadows go off to the right and slightly up where as the shadows from the balls are down and to the left.


03-27-2003, 09:48 AM
Hi Mr Rios,

To add to Spankdaddys post here is a quick image I did a few months ago using the FPM technique for the shadow and also using the bkgd image as a reflection map. That is what you need as a minimum to blend your CG in with video.


03-27-2003, 08:21 PM
Another possibility is to use compositing software. I have a rough test animation I did about a week ago, I'll try to get it posted soon. Here is what I did:
*Note:this shot was done as a lock down, no camera movement

First thing you'll want to do is buy or make a matteball. I made mine out of a 6" styrofoam ball then I covered it in a light gray spacel. You'll use this to help you match the lighting.

Second: Get your tape measure! Take as many measurements of your set as you can! How wide is the set? How long is the set? How high? Where are your light sources? How are they angled? Where is the camera in relation to the set? Where on the set is your matteball? How high up is it? What's it's distance from the light source? This may sound anal, but the more of this type of information you have, the easier time you're going to have.

Third: Shoot your video.

Fourth: Remember all those measurements you spent so much time taking? Now in LW build a rough representation of your set. Let me stress that this does not have to be pretty, you're not even going to render it, so don't spend too much time on it. Don't forget to build a virtual matteball and place it in aproximately the same position as it is in your footage.

Fifth: Duplicate your light sources from your video in your virtual set. To get the colors right, use a frame from your matteball video. If tour trying to match the color for your key light, position your color picker over your matteball where the key light hits it. Do the same for the other lights. Now tweak your lights until your virtual matteball looks like the real one. You may need some additional lighting to accomplish this so experiment a bit and do some test renders.

Sixth: Now if you're happy w/your lighting get ready to render. Set evrything but the object you want to add to the video to be unseen by camera(I believe this is under the objects properties). Render!

Last: In your compositing software, load up your video and your 3D footage. Place them both in the timeline on different layers, make sure the LW layer is on top. Now you'll have to render out this composition as well, but if you scrub the timeline you can see what the end result will be. The big advantage to this approach is that you have some flexibility w/what you can do w/the footage now. Rendering motion blur in a program like Adobe After Effects is quicker than if you rendered it in LW. If you rendered out a complex object in multiple passes you can make subtle changes w/o having to re-render the entire shot. If your reflections are to sharp, go to the reflection layer and blur them a bit. You could even seperate the lights and render them as seperate passes. If your Fill looks too bright, pull that layer down in the comp.

This is the approach I took and its not the only one, but I thought if I went through it step by step it might help you out. If I've skipped anything or oversimplified anything, then anybody out there point it out! I'm still learning too and could use your input.

03-28-2003, 10:46 AM
There's dedicated software that sfx companies use to blend 3d with 2d footages seamlessly. All the greatest SFX houses use Boujou or Matchmover or 3d equalizer. 3d Equalizer was used in Lord of the Rings trilogy.

03-28-2003, 12:24 PM
Can't seem to upload footage. Anybody have any ideas. I rendered an animated gif but when I submit it says it can't connect to the server.

03-28-2003, 12:30 PM
Ok here it is

03-28-2003, 12:36 PM
Ok here it is

03-28-2003, 11:24 PM

03-28-2003, 11:50 PM
this is it

04-02-2003, 06:03 PM
One thing you could do instead of rendering with a blue background and keying out the blue in Premiere is render out in a format that outputs an alpha channel. A couple of formats are the Tiff32 or PSD32. With the alpha channel added you will have a much cleaner keyed out background. Also the alpha channel will be able to control any transparent areas like a glass surface that isn't totaly transparent and make them semi transparent. Of course you will have to render out to frames doing it this way and create your media file in Premiere or whatever Digital Editing software you use.