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sIBL and Ground planes (for shadows only) (Read 2799 times)
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sIBL and Ground planes (for shadows only)
01/31/12 at 11:34:41
Hi all,

So I have another newbie question...Now this may be a more general lightwave question if so tell me to go away and ask on the newtek forums....

I recently watched this video showing how HDR Light Probes used to be done in LW9.6 without sIBL plugin.  It's mostly redundant now, except at 14 min 20 sec he demonstrates how to set the background image as a front projection on the ground plane to disguise it during render (tweaking luminousity to blend it in, which I'm sure will have some of you screaming at the implication for the lighting Cheesy)

However, it does effectly remove the ground plane leaving only the shadows.  This only works as the background is a flat 2D projection that he aligns the scene with, so I'm sure you know my question now...

* Drum roll please *

How would you achieve this affect using a sIBL full spherical background?
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« Last Edit: 02/01/12 at 10:04:26 by N/A »  
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Re: sIBL and Ground planes (for shadows only)
Reply #1 - 02/01/12 at 21:50:20

Two ways:

- You can prerender the background ball. That gives you a fake 2D background plate, that you can frontproject back into the scene.
- You can place the background ball EXACTLY at your camera position. Then you can do a spherical projection on any geometry, and it will look correct.

Oh, and the third way is actually implemented in sIBL: Use a shadow catcher. LW11 now has a new shadow catcher material, but the ground plane that sIBL sets up works just as well. That gives you a pure shadow on the ground plane, the rest is transparent and shows the background ball behind. Sometimes you have to open the Nodal Surface of the shadow catcher and play with the brightness and contrast of the nodes (they are commented)


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