First Time Compositing, Help!

[ggoerl]

So lets say I have this basic footage of just panning across my desk from left to right and I want a legoman to run across it.
I design a legoman in c4d now what? I dont know/understand the whole compositing method.

[Huy Vu]

The perspective will be tricky. I would render out the 3d animation as a file with a blue or green background that you can key out in After Effect. In AE, use Keylight (it's a plug in that comes with the program) to get rid of the background. Put the shot of your desk underneath the 3d movie and move the Lego man so that it seems like he's on top of the desk. Problem is the pan, you'll have to match his movement so that it doesn't look like he's standing still while the background is moving. Maybe you can track the motion of the pan and apply that movement data to the Lego man so that it seems like he's moving too.

[ggoerl]

oh is that all? I thought it would be way more technical than that. Im familar with ae and keylight thanks for the info.

[Matt Grunau]

What you are wanting is a pretty tall order. Firstly, unless you have motion tracking sofware, leave the camera in a static position. Trying to folow camera movements my hand to fit the 3D camera's render is no small feat.

First, setup you camera and animation and with a still of the footage as a badkground to match the angle of the table and the angle of you 3D camera.

Second, then render with a Multipass setup so you can really tweak what you want and dont want in post.

Third, render out in a format that supposrts alpha channels. .png and .tga will work.

Fourth, render the main subject and shadow layers seperately (you will have to set up a ground plane in your 3D app, set it white, and have it 1 either with an alpha channel (should do anyway) and 2 on the whitest ground plane you can. That way you can use the shadow renders and simply use a blendning mode like Multiply to composit them.

Fifth, make sure your lighting in your 3D app matches the lights around it, for acurate shadows, and to decrease the amount of color correcting you will have to do on the render to make it fit (if your indoor lights are colored in any way, have the 3D lights the same (one good way to fins out is to place various white objects around the place you will film, and with you video camer, film each light source, and then with Photoshop or any NLE, get the color of whe whitre ofjects of what you filmed and you will be able to set up your lights with the right colors.

Sixth, accurate shadows are important, as is the principles of light. You may have to use area lights (in your 3D app) to get "shdow blurring" as if goes away from the subject.

Seveth, the lighting fallof from each light source needs to be noted and each 3D light needs to have that falloff the same or close.

Eigth, Make sure the motion blur in your 3D app is the same as what you are filming. A shutter speed of 1/60th shot in 20p or 60i will NOT match the motion blur of your 3D app if it is set to 1/48th, which would 24p.

There's even more, but my brain hurts.