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Vray - Matte/Shadow shadows and reflections pass
show user profile  xandos
Hi guys, I have an environment which I have already rendered out, and want to composite a character over the op. The tricky bit is that the floor is a bit reflective, so it would be great if in the character pass I could include shadows AND reflections. I have tried using the VRayMtlWrapper, changing to matte surface, playing with Alpha contribution (reading suggested -1.0) and checking shadows etc. The problem is, that it seems to only have an alpha channel for shadows, and reflections are ignored? ie you only get reflections where there are shadows...

Could anyone suggest the best way for me to go about this?

Many thanks for reading!

Here's a picture illustrating the problem, basically I wan the reflection to have some sort of alpha...

read 10450 times
7/5/2010 1:00:51 PM (last edit: 7/5/2010 1:29:46 PM)
show user profile  xandos
Just in case anyone needed to know how to do this, I wound up doing it as a render layer without alpha, just white materials to pick up the shadows and reflections, and then composite it on as a multiply layer..
read 10420 times
7/6/2010 5:32:43 PM (last edit: 7/6/2010 5:32:43 PM)
show user profile  Joey Parker Jr.
Good solution. This has been an issue with VRay all along.
 photo 2012-sig_small3_zpsbd114b69.png

read 10411 times
7/6/2010 6:29:30 PM (last edit: 7/6/2010 6:29:30 PM)
show user profile  Clemente
Just brainstorming... if you're doing a still image (not an animation) you could render your character or object that you want a reflection of and create the reflection in Photoshop. You can do this by duplicating the character layer, mirroring it (over the horizontal) and then adding a gradient mask and lowering the opacity...
read 10396 times
7/6/2010 10:28:52 PM (last edit: 7/6/2010 10:28:52 PM)
show user profile  Bolteon
worst idea ever.


i dont see this so much as a problem with vray but rather people just being lazy about making another pass (no you should never combine shadow and reflection passes together as a single render unless your doing some good trickery with render elements).

just turn the reflective objects to matte objects, and render against black. then comp.

-Marko Mandaric

read 10392 times
7/6/2010 10:36:41 PM (last edit: 7/6/2010 10:41:21 PM)
show user profile  Joey Parker Jr.
"just turn the reflective objects to matte objects, and render against black. then comp."

OK How do I save just the reflection from this render so that someone can drop it into another scene
with a different color bkgd and have it look real?

 photo 2012-sig_small3_zpsbd114b69.png

read 10386 times
7/6/2010 11:01:16 PM (last edit: 7/6/2010 11:01:16 PM)
show user profile  Bolteon
that would go something like this:

render the bg (main object set hidden)
render the shadow (object not visible to camera, bg set to matte object with alpha of -1 with shadows on; the shadow is your alpha)
render reflection pass (bg as a matte object [not shadow and alpha] with the main object invisible to camera but visible to reflection)
render the object (bg set to matte object or invisible to camera if it doesn't clip the main object)

always remember to render on black no matter what the pass it (as in the env color should be set to black in max)

then your comp goes (top to bottom):

main object

boooyaaa. that's how the big boys do it.

-Marko Mandaric

read 10378 times
7/6/2010 11:30:16 PM (last edit: 7/6/2010 11:35:49 PM)
show user profile  Joey Parker Jr.
Thanks! I shall give that a try.
 photo 2012-sig_small3_zpsbd114b69.png

read 10375 times
7/6/2010 11:33:38 PM (last edit: 7/6/2010 11:33:38 PM)
show user profile  xandos
Thanks Bolteon, I guess I was being lazy trying to get both in one pass (It's in stereo so every pass is two passes anyway)... It worked but it's not that clean, yours does indeed seem like the way to do it...
read 10360 times
7/7/2010 1:59:28 PM (last edit: 7/7/2010 1:59:28 PM)
show user profile  del3d
read 10356 times
7/7/2010 2:18:27 PM (last edit: 7/7/2010 2:18:27 PM)
show user profile  Clemente
Wow... I nearly lost some of my forehead as the solution wizzed over my head at top speed. You guys are wicked smaaat (as they say in Good Will Hunting).
read 10325 times
7/9/2010 4:27:15 AM (last edit: 7/9/2010 4:27:15 AM)
show user profile  Joey Parker Jr.
Thanks again to Bolts. Worked out perfectly.
 photo 2012-sig_small3_zpsbd114b69.png

read 10223 times
9/8/2010 12:22:03 AM (last edit: 9/8/2010 12:22:03 AM)
show user profile  Bolteon
cheers, glad you nailed it.

-Marko Mandaric

read 10210 times
9/8/2010 1:53:09 AM (last edit: 9/8/2010 1:53:09 AM)
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