Compositing Issues

Most professional productions have moved to trying to get everything looking right, "in camera," within their 3D package of choice, and moved to layering things together in a compositing package. This allows for tweaks to 2D pre-rendered image layers/elements that require only a few moments to compute, as opposed to the minutes/hours/days often required to re-render complex 3D Scenes.

If you take a look at the final render above, again... you'll notice that the Radiosity Dome is still visible behind our Character. If you try to layer this image onto a background or other rendered layers, you'd get a funky, multi-colored "halo" around the character, even with an Alpha channel to isolate it from the Background. This is because most modern compositing packages assume that the images with which they are working, have had their colors already multiplied with the values of the Alpha channel, and most modern compositing packages are built on the assumption that the background color behind the rendered images will be black.

So... in order to yield a workable image for a pipeline that incorporates compositing... you've got to inset another dome, surfaced black, just inside the HDR lighting dome that the camera will see, but will not affect the casting of rays that LW is using to calculate its Radiosity lighting solution.

(Click Image For A Larger View)

HDRI_F.lws already has this set-up for you... with a slightly smaller dome called "Pre-multiply" as a child of the HDR_Dome object visible only as Vertices, (so it doesn't get in the way of you aligning your Objects in relation to landmarks on your HDR Dome).

The Pre-multiply dome's Surface Color is set to 0,0,0, and 0% diffuse/luminous. And on the Advanced Tab, its Alpha Channel needs to be changed to Constant Value, and its Alpha Value set to 0. This is what gives us our black background, and black (transparent) alpha value behind our opaque (white) character.

In order for this Pre-multiply dome to be seen by our camera, but not intercept the rays cast by our HDR dome, we have to set it to be Unseen by Rays. It should also have Self Shadow, Cast Shadow, and Receive Shadow, all un-checked.