Live Action and CG integration

[wim.mutsaers]

I am trying to create a basic shadow catcher material.


First Scene:

When I use a Dome Light with an HDRI it works great with vrayproprieties into a "shadow catcher" plane as you can see in the first image.
The second image is just the gi contribution of the matte that gives a "strange result".

But in this exemple: Sucess!







Second Scene:

Here I created a basic geometry to represent the HDRI and then I projected the HDRI with a spherical projection node into a vraylightMtl. I have GI lighting the scene from that Geometry with an hdri.

This way I get more correct lighting and reflections (I guess)


But in this exemple: NO Sucess!

The first image shows that when I remove the GI contribution from the matte surface proprieties, I get no shadows/occlusion.
In the second image I leave GI contribution on but get that "strange result". BUT I get some shadowing/occlusions.







How can I get the second scene to catch shadows/occlusion but not that strange result?

NOTES
-I am using Irradiance Map + LC in both scenes with basic settings.
-There is some basic info attached to the images like the alpha and the environment that may help to solve the problem.



Thanks in advance

[RobPhoboS]

Same problem I'm having as here:

http://www.chaosgroup.com/forums/vbu...override/page2

Can't quite work it out either.

[wim.mutsaers]

Tnks Rob.

Well. Vlado said in that thread to use the environment overide with the screen mappint but it gives the same result as with the imageplane.
At least in my scene.


Maybe this illustrated examples from my scene will help Vlado and guys solve this.

[vlado]

When you are using a dome light in conjunction with GI and matte objects, make sure that you override the GI environment with a black color. Otherwise, the matte shader will think the scene is normally lit with the GI color, when in fact it is not.

Best regards,
Vlado

[wim.mutsaers]

The dome light exemple is working for me.

My main issue is with the second scenerio when there is no lights, only GI coming from the geometry mapped with an hdri.

Is there a solution for it Vlado?

[vlado]

Is it just mapped through a VRayLightMtl material?

Best regards,
Vlado

[wim.mutsaers]

Yes, I am using a vraylightMtl, I had try with a surface shader but it's the same. I know the environment thing is somehow the issue.

I think the problem is that the matte surface works with lights casting shadows, and not with geometry illuminating with an hdri. It just that I really need this casting shadow thing to work with geometry.


Tnks.

[wim.mutsaers]

btw, I did try to convert the geometry to a "lightmesh" and mapped this with the HDRI. It works, but the resulting illumination is not what I was looking for. Far away from the domelight result and the mapped geometry.

The shading network.

[RobPhoboS]

make sure that you override the GI environment with a black color.

Sorry to sound stupid but I want to ensure I understand correctly. Do you mean in the 'Environment' section of the Render Settings window, or do you mean in the material override for the matte ground ?
I've tried popping the same black checker texture in both but it doesn't appear to work for me.

[wim.mutsaers]

No more news about this?

[vlado]

I'm not sure it will work like that; the matte/shadow functionality is based on shadows from actual light sources and the GI environment. It won't work with mapped geometry (unless it's a mesh light, but then there would be other issues).

There are of course ways to get what you need, but they require several renders (see f.e. http://www.spot3d.com/vray/help/200R...nim.htm#basics which describes a general way to put any object into any scene, no matter how it is lit).

Best regards,
Vlado

[jasonhuang1115]

btw, I did try to convert the geometry to a "lightmesh" and mapped this with the HDRI. It works, but the resulting illumination is not what I was looking for. Far away from the domelight result and the mapped geometry.

Can you post the difference? I am kinda curious. If after converting the geo to a lightmesh and mapped with the HDRI works, then that should be the correct lighting and shadowing result you should get from the lighting setup. The result technically should be somewhat different than with a domelight plus mapped geometry depending on how you set it up as domelight is essentially an infinite sphere and your mapped geo provides the correct spatial information of lighting.

[wim.mutsaers]

Well the lightmesh result just makes shadows very strange (not really correct I guess) , it doest work well really. Like Vlado said, there are some issues associated with it ( not sure which).

Vlado: Why not a shadow catcher shader like "mip_matte_shadow" ? That can catch GI, AO and reflct/glossy?

I remember in those Scott Metz. videos about vray/ptex/Mari workflow. How would he composite the cg objs in the plate/footage (let's say he had one) since he is also using a mapped geo vraylightmaterial with HDRI?


Tnks a lot

[vlado]

Vlado: Why not a shadow catcher shader like "mip_matte_shadow" ? That can catch GI, AO and reflct/glossy?

Are you sure that works with GI coming from a self-illuminated material (not the environment)? From what I remember, it doesn't, so it won't help in your case even if we did that.

Best regards,
Vlado

[wim.mutsaers]

Well, I cant be sure right now, I remember doing some tests last year and it worked, not sure if it was geometry lighting. I will test as soon as I have some time and post here.

Tnks for your reply.