Microfilmmaker Magazine - Tips & Tricks - Compositing Lightwave Models with Lightwave 6


	Compositing Lightwave Models with Lightwave 6 - 9.5

by Mike King

3D compositing can be extremely challenging but at the same time, very rewarding. Unfortunely, one of the difficult parts of compositing is to create a format that is usable in a variety of editing environments. Lightwave's alpha channel is an exellent way to do this even if making a "perfect alpha" is quite tricky. The problem with alpha channels is that when an image is rendered using motion blur, DOF or even anti-alias, whatever background information was used during the render, the edges will contain color portions of that because of the way that render passes are mixed together. Another difficulty is casting shadows onto a background image without damaging the background. Here, we will explore the basics of compositing and specifically look at how to create shadows and matte objects that don't interfere with the composited image.
The first thing we need for our 3D composite is a background image. Obviously, you would want video as the background (hopefully the camera was still for ease) but for this tutorial, an image makes things manageable. If you don't have one of your own, download this picture I took of a great snorkelling island at Puerto Vallarta. The first thing we need to do is deside what objects you need to composite from the picture. Here, you need to trace the island so that you can create it as an object and also create a simple plane for the ocean water. Make your plane first and save it. Then there are two ways to create the island, you could trace the island in Modeler from a background image or you could magic wand the sky away in your favorite paint program and then use that new image to clip away another plane in layout.


Method 1: Trace a Clip map in a paint program using fill and magic wand so that a 2D island can be used in Lightave as an object with very accurate edges.	Method 2: Trace the actual image in Modeler to create an outline of the island as a real object. Use the pen tool to do this.

OK, are you ready to composite? Load your ocean plane and your island objects into layout. Also load the island image into the background and show it in the camera view. You need to set your ocean plane size large enough so that you can cast shadows onto it and so that it appears in the area of the ocean water from the image.

Its tedious trying to visually line up perspective and positions of these stand-in models but if they are kept simple and you attempt to position them similar with respect to the position of the real camera from the background, you can get it to be quite accurate. Ideally, you would have been on set and recorded all the measurements for positioning your stand-ins later with much better accuracy, but this isn't always possible.