Vray Shadow pass

[breader]

Hi,

I am trying to produce an alpha channel of shadows only or a pass with only my shadows!, I am quite new to VRAY so A bit of an explanation would be appreciated if it is at all possible.

Many thanks in advance.

[Morbid Angel]

you may approach it in few ways:
1 - apply single vray material wrapper to the entire scene, and specify to render only shadows, if you set alpha contribution -1 the returned result in alpha will be shadows only.
2 - you can apply a single vray material to the entire scene, take all your lights, set their intensity to 0.001 and shadow color to full white, this will also return shadow only in render.
3 - you may play around with render elements shadow passes, they also generate shadows, but often we use custom shadow passes created with methods above.

[Jynks]

I can not seam to get this working.... I wish to render just the shadows with an alpha for easy compositing.

I have tried both methods.

Could you please explain in more detail...

I have a simple scene illuminated with a single light and a GI LC on both bounces.

This is the render


If i click OFF "use global settings" in the lights "shadows" drop down thing... i get this... but it looks wrong?


This is the method as i understand it from your description using the lights at .001 etc etc


This is the method using the vrayMltWrapper method as i understood it from your description.


As you can see neither is rendering just the shadows on the render.. and neither is showing just teh shadows on the alpha map.

I am using rc2 and max2009

Any help would be appreciated.

[Jynks]

This is the redner element - vray_matShadow...


So I guess this is the way to go.... but tthe alpha is still like in the other pics i posted.,... i am not getting the alpha of just teh shadows.... semi transparent and such?

[RErender]

is the alpha contribution of the matte set to 0 or -1?

[dapeter]

In the VrayMtlWrapper, uncheck 'No GI on other mattes' - that made it work for me.