3d effects over traditional video?

I want to learn how to use blender for visual effects, and I’m a little stuck.

I want to be able to make a simple 3d mesh of an object I have, video tape the object, then use blender to make an object roll next to it, and maybe reflect some light on it… does that make sense?

The idea is to have 3d objects changing the lighting scene of a 2d video.

I’d assume I would have to model all of the objects I want to be affected, but I don’t want to replace items with 3d models, just let the 3d models receive the effects, then pass the effect on to the real image beneath…

Does this make sense at all?

picture neo when he touched the miror and it got stuck to his hand and started covering his arm…

That sounds interesting!

I saw a video before, kind of what you are looking to do.

It was a butterfly rendered in a 3D program, then it was super-imposed onto a real video of a kid. the butterfly flew onto the kid. The neat thing was, it looked like the butterfly was actually there. Shadows on the kid too.

How did they do that?

I assume that they used an Alpha Chorma-Key method to get the butterfly into the real video. But the method of placing the butterfly’s shadow on the kid’s body is unknown to me.

Maybe they took the real video and re-enacted the kid’s body. Made a 3D mesh of the parts that will have a butterfly shadow. Saved the video of the shadow only and used an alpha channel on the real video to show a shadow.

Just use a MAT OnlyShadow for the Kid which receive BFlyShadow !!!

yet another tutorial needed to go with the SE. i tell you the power of blender is still not realized.

Okay, so now I’m going to start playing with the OnlyShadow thing, but I’ve got a more basic question.

Let’s say I have a video file of my arm, and I want to make it look like I’ve got some cool/cheesy weapon… Let’s say the spear from Alien Vs. Preadator, how can I do that and have it oversampled?

If I add a scene, is it possible to make the background transparent? I want to have the object rendered over another video, not even worrying about shadows just yet. (I’ve thrown a scene onto the SE above a recorded video, but all I get is the rendered scene, and when I do chromakey I get jaggies)

Okay, I just found this:

While it doesn’t answer all of my questions, it does help a lot!



Here’s a little more thorough explanation of this very useful technique…

When a material is ShadowOnly, it does not appear on-screen but shadows can be cast onto it. Therefore, what you see in the result is “the shadow only.”

In your 3D segment, create an object that is approximately the size, shape, and location of the object from the video segment. (Superimpose a shot from the video as your background for reference while you work, then remove it.) Assign this object a ShadowOnly material. When you render your scene, the ball will roll into the scene and cast shadows upon The Invisible Man. This shadow information is what we want.

Render your scene in a format that has an Alpha channel. (RGBA, a file-format such as PNG or TGA, Premul setting.)

Bring the video and 3D together in the video editing application of your choice (or Blender), using AlphaOver. Now you will see the shadow appearing to be cast upon the video object. You will have to tweak quite a bit to make it look convincing: your eye will want to believe it, but you need to be sure nothing “jars” its sense of belief.

Now that is friggin COOL! Thanks!