Subject: Re: Reflection images and low light...
From: Andrew Hofman <[email-masked]>
To: Multiple recipients of list <[email-masked]>
Date: Sat, 23 Dec 1995 16:25:25 -0500

At 10:02 AM 12/23/95 -0500, you wrote:
>Hi all,
>
>I have a problem...
>
>A scene contains an object which is supposed to be metallic, so it has a =
>planar image as a reflection map.
>
>This object is lit by a single spotlight, the cone angle envelope =
>controlled to start as a pin and then widens out. The ambient light =
>intensity is set to zero.
>
>The idea is to have this spotlight playing over the surface of the =
>object which is otherwise in complete darkness.
>
>My problem is that even with the spotlight intensity and cone angle set =
>to zero, the object is still visible. If I remove the reflection map, =
>everything's fine. I don't want to have to use a crumple bump map if I =
>can avoid it.
>
>I hope someone can help...
>
>Simon
>

Sounds like a job for alpha channels!

1) Render out a still of your object, fully reflective.

2) Using this as a background reference only, animate a black ball with all
surface attributes set to zero, except Edge Threshold. Make it grow larger
over a hard white background. With transparent edges, it will look like a
fuzzy black disc -- the negative version of a spotlight. Adjust Edge
Threshold for desired fuzziness.

3) Save this out a seperate animation.

4) In a new scene, load the object's still once again, this time as a
visible background image.

5) Load a hard black still as your Foreground Image, and the ball animation
as your FG Alpha Image sequence.

6) In the resulting animation, hard black will conceal everything except
where the negative spotlight is "shining".

There are a couple other ways to do this, but I chose compositing because it
works well in such cases and doesn't take much processor time.

  
Andy Hofman
LumaQuest Productions           
Animation -- Dual Raptor 3 Rendering  
[email-masked]
513-643-7333