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matte shadow alpha and background
show user profile  Mayhem
Hey guys,

Here's a thing i've been trying to figure out for a while...

I need a matte shadow material to reveal the background but i also need the environment image not to show up in the alpha channel?

What do you guys reccommend i do?


read 642 times
4/14/2008 6:13:16 AM (last edit: 4/14/2008 6:13:16 AM)
show user profile  mrgrotey
Save as .png

[edit] hmm may have gotten the wrong end of the stick

read 634 times
4/14/2008 6:15:45 AM (last edit: 4/14/2008 6:29:28 AM)
show user profile  Bolteon
what would be the point of the matte shadow showing through the bg...?

why not just save as an exr/tga/tiff and then comp it over your bg plate in photoshop?

-Marko Mandaric

read 628 times
4/14/2008 6:24:27 AM (last edit: 4/14/2008 6:24:27 AM)
show user profile  Mayhem
Is it possible with exr? I'm trying to render a z-depth as a layer in my exr file and i'm experimenting with a 32bit workflow.

read 626 times
4/14/2008 6:26:55 AM (last edit: 4/14/2008 6:26:55 AM)
show user profile  Mayhem
Ok let me explain some more...

I've got this animation of a television i want to play some movies on with a plugin in after effects.

So i render uv-coords in a seperate image sequence. The uv-channel is on the exact same place as the screen of the television. The plugin knows how the skew the image by the info of the uv-coords and it plays the movie on the same layer as the uv-coords in after affects. (This is the part that works fine)

Now i render the television with on the place of the screen the matte material and before the matte material i've got the glass of the television screen with a low opacity. (This is the layer that goes on top.)

I'm rendering this image i'm testing with and the matte material works fine but the background doesn't show because it's black in the alpha channel.

(I prefer to use exr because it gives the possibility to render z-depth as a layer and i'm experimenting with a 32bit workflow)

read 614 times
4/14/2008 6:55:36 AM (last edit: 4/14/2008 6:55:36 AM)
show user profile  mrgrotey
ah so you're saying the opacity of the screen glass doesnt affect the alpha? ive had that before with the raytrace material, really annoying. maybe doing separate passes is the answer?

read 606 times
4/14/2008 6:59:39 AM (last edit: 4/14/2008 6:59:39 AM)
show user profile  Bolteon
can you post up a couple of images... i think i understand what your getting at but could use an image to make sure. also, what r/s to make sure.

exr's can carry the zdepth as a layer, though in after effects having it in a layer or outside as a seperate stack doesn't really matter. you can enable the depth in your render elements.

-Marko Mandaric

read 604 times
4/14/2008 7:00:33 AM (last edit: 4/14/2008 7:02:16 AM)
show user profile  Mayhem
@grotey i'm not sure we understand each other.
"ah so you're saying the opacity of the screen glass doesnt affect the alpha?"
That's seems to be a good thing to me :)

Here's an image. The white represents the alpha channel. The small white square is the television. The one and only thing i need is the background to show in the render. (I hope it's something stupid i forgot)

I'm using mental ray 3.5

read 590 times
4/14/2008 7:30:02 AM (last edit: 4/14/2008 7:42:55 AM)
show user profile  Bolteon
do you want to show the bg behind it to fake a reflection of sorts on the glass?

-Marko Mandaric

read 578 times
4/14/2008 7:44:58 AM (last edit: 4/14/2008 7:44:58 AM)
show user profile  Mayhem

read 575 times
4/14/2008 7:45:45 AM (last edit: 4/14/2008 7:45:45 AM)
show user profile  Bolteon
why not render out a seperate pass of the glass with a raytrace for reflections and screen it over your comp in after effects... it'll look tons better and you wont have to hack your way around it.

-Marko Mandaric

read 566 times
4/14/2008 7:57:17 AM (last edit: 4/14/2008 7:57:47 AM)
show user profile  Mayhem
Found a solution, put a sphere around the entire scene with a matte shadow material. Opaque alpha = on, shadows = off. Gave the sphrere a object id of 2. In my occlusion material i gave a object id of -2 in the incl/exclude object setting. And it renders the alpha the way i want it.

Thanks for the replies. No solution but i appreciate it.

read 517 times
4/15/2008 4:26:22 AM (last edit: 4/15/2008 4:26:22 AM)
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