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000752_owner-lightwave-l _Wed Apr 26 13:01:54 1995.msg
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To: lightwave-l@netcom.com
Subject: Re: shadows on live
From: ggarramuno@sicoar1.satlink.net (Gonzalo Garramuno)
Message-Id: <6J654c1w165w@sicoar1.satlink.net>
Date: Wed, 26 Apr 95 01:20:04 ARG
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In a message
JB>Okay, here's my trouble: I'm going to be doing some LW effects for a
JB>student project where I need a 3D object to move around in a real-world
JB>setting, and cast shadows on the floor (the scene is to take place in a
JB>garage).
JB>I know how to use front-projection mapping on a dummy object so it will
JB>be in the place of a real-world object (i.e. a 3D floor object matched
JB>with the real floor), but I need shadows on this floor. To get front-
JB>projection-mapped surfaces to match a background image, they have to be
JB>100% luminous, with no diffusion. Unfortunately, they won't receive
JB>shadows this way...at least not shadow maps.
Justin,
This is a problem with the way Lightwave handles surface settings which I
mentioned to Allen Hastings (LW's programmer) several months ago.
Right now, the easiest solution I know will take time, and it may not work
in all situations. First, set up a plane completely luminous with a front-
project mapped image (to work as the ground). Then place your objects and
animate your scene. After you are 100% sure of the animation, set up the
lights until they match what you expect. Don't worry about the projected
shadows yet.
After you are done, play around with the surface settings. Lower the
luminosity from 100% while at the same time you increase the diffusion from
0%. After that, set the object edges to transparent and also start
changing the Edge Value setting.
Eventually you will find some good numbers (in my case, it took me around
4 hours for one scene). REMEMBER! If after you are done, you decide to
change/move/add lights, you will have to repeat everything again.
However, if your lighting changes during the animation (or you move your
camera) this method will not work.
In that case, you will need to render your scene twice and composite
the shadows later. To do this, you will need a program like Image FX (I
belive better for this) or ADPro (you may need to use ARexx or use something
like ProControl).
First, you will render your whole scene with no shadows turned on (and no
plane -ground). After that is done, load your ground object or those that
need to receive shadows. Make all surfaces of all other objects 100%
white, and 100% diffuse and 100% luminous. Make your background also 100%
white.
Then, select the surfaces of the objects that are going to receive the
shadow and also make them 100% white and 100% diffuse, but set luminous to
0%. That way, shadows will be rendered onto those objects.
After all that is done, render the animation again, but with shadows
turned on now. If everything went all right, you will end up with a white
image, with some gray or black places where the projected shadows are.
Now, you should go to your favorite image processing program and load the
shadows animation. You should extract a mask for all the gray areas
(consult your software manual to do it). The easiest way is to copy (or
load) that same image as an alpha channel (or mask). If copying the image
directly to the mask makes the shadow to dark or too white, you should play
around with the contrast and brightness settings of the image before
copying it. Then, save another sequence of images, but of the mask only.
Finally, you should composite the shadow sequence on top of the rendered
sequence with the corresponding alpha channel (mask).
If this is not clear, e-mail me and I could give you more detailed
instructions.
Gonzalo Garramuno
ggarramuno@sicoar1.satlink.net
Carlos Sorin Cine S.R.L.
Buenos Aires, Argentina