Black render Keep alphas

[mouton007]

HI all

i am trying to get a pure black render to create a fog pass etc but once i insert the bacl VrayMTl in the override slot in the vray settings i lose all my leaves an plants oppacitys is there a way to retain them ?

Regards
Mouton

[urbanite]

Keep asking for solution for some time.. I would love to know the trick too.

[fixeighted]

You can exclude objects, so do that with all your leaf objects and make a material copy that has the opacity used on a black diffuse. Would that not do it?

[urbanite]

I believe it is not working with fog.

[fixeighted]

I must be missing something. Can you explain exactly what needs to happen and what the render should look like ideally?

[mouton007]

yeay that can work but i am looking for a faster solution i have a lot plant shader in my to replace them all with a material copy would take to long

You can exclude objects, so do that with all your leaf objects and make a material copy that has the opacity used on a black diffuse. Would that not do it?

[fixeighted]

I'm glad that works for you. Some things just take time
All you need to do is use colour corrections on the maps, so seconds per material really.

[mouton007]

I'm glad that works for you. Some things just take time
All you need to do is use colour corrections on the maps, so seconds per material really.

maybe i should just setup material switches will take tim but then its setup

[fixeighted]

Absolutely, if you do the same thing regularly then once it's done it's done

[mouton007]

is there a script so that i can globally make al the vrayswitchmtl to the second material in it ?

[fixeighted]

Hmm, I can't think of one but I'm sure there's someone on this forum who could suggest a way to do it if it's possible.

[Joelaff]

Would be way cool if the VRayMtlWrapper could have a special mode when used in the override slot so that it would act as though its input for each material was the material prior to the override. So you could easily set up matte objects like this all in one place.

You might see if you can use the right-click vrayproperties settings (Select objects, right click in the viewports, choose vrayproperties bear the bottom on the lower right menu) to select all your trees and then change the matte object settings in that dialog. I have not done many matte objects that way much; so I am not sure of what the limitations are. There is some kind of matte objects control there.

Also you could try turning off all lights and GI and just using luminous fog that way. Or perhaps a simple Zdepth channel could achieve the fog effect you need. You would composite it in the post.

Good luck.

[vaya_studio]

mouton007 You don't really need a black beauty render, just use the VRayAtmoshpere render element. For the rendering I usually desable everything that won't contribute to the volume light from the VRay Global Switches tab: reflections/refractions, displacement, etc. If you dont need it you can desable GI as well. You can assign a black material in the Override material slot and exclude the objects with alpha from the list.