Render Layers

[Infrared digital]

Hi

I am rendering some CG characters to be merged with live action footage and want to have the shadows (with alpha) for easier compositing. To do this in the past I rendered the character in one render then, the shadows in a second render using the override material applied to the ground geometry to capture the shadows - is it possible in VRay 3 to do this in one render ?

Or is there a better way of doing this ?

Thanks

N

[Morbid Angel]

Its possible to do this in one render but you will always have the character overlapping the shadow, and typically in comp they like to control the shadow separately but because you have the character rgb and shadow in one buffer (layer) its not possible.

In 3ds max, you now have state sets which essentially can capture various changes to the scene and record them. So you can make two state sets - one character with ground plane visible to camera off. Another with character invisible to camera and ground plane on with alpha -1 and matte checked.

To me this is the most satisfying method (for comp) to get the job done.

You might have to render direct and contact shadow also for better integration.

[Infrared digital]

I have been looking into State Sets but to have the character and the shadows as two separate layers - will that not require two renders ? I'm pretty sure it does.

It's a shame that vray can't render geometry in layers in one render - Modo does it but I am too invested in max.

[Morbid Angel]

yes its two separate jobs. Not sure how modo works. The shadow pass is not an expensive render though.

[Infrared digital]

Your right, it isn't an expensive render unless you have 20 or 30 shots then it becomes expensive in Vray and post.

Incidentally Dmitry, do you use Nuke ?

[Morbid Angel]

Your right, it isn't an expensive render unless you have 20 or 30 shots then it becomes expensive in Vray and post.

Incidentally Dmitry, do you use Nuke ?

yeah I do.

To me though, its what I have to do to keep the comp happy and ultimately get the show finished

[Infrared digital]

In Nuke, I am trying to comp together the vray render passes including the raw passes so that they look exactly like the RGB render - but I can't get it right. Do you have a tutorial or guide that would tell me how exactly to do it ?

It's very frustrating because the result I am getting is almost there but not quite.

[Morbid Angel]

Yeah unfortunately I can't get them right either using raw. Its a bit odd as I remember it working, I even emailed chaos a simple case.

What you can do though, is use regular passes, like gi/lighting or light selects with diffuse/specular modes, and in comp extract the raw by diving the light with the diffuse. Essentially this produces accurate raw lighting/gi then you can control it and at the end of the graph multiply it by the diffuse again to get the passes to rebuild accurately.

[svetlozar.draganov]

In Nuke, I am trying to comp together the vray render passes including the raw passes so that they look exactly like the RGB render - but I can't get it right. Do you have a tutorial or guide that would tell me how exactly to do it ?

It's very frustrating because the result I am getting is almost there but not quite.

Can you should us what is the difference between both?
Would it be possible to also send us the Nuke composition along render elements for investigation?

[Infrared digital]

Hi Svetlozar

I will send all the info when I get back home. I am using Nuke Non-commercial so the script won't open on a full version of Nuke so, I will send screen grabs and the renders.

I appreciate you picking this up.

N

[Morbid Angel]

Hi Svetlozar,

Please see attached maya 2015 scene using V-Ray for Maya version 3.15.01, revision 26280 from Sep 24 2015 as well as nuke 8 script rebuilding the elements. In my case, rebuilding using raw light selects +raw gi does not = rebuilding using raw light + raw gi. Perhaps there is an error in my logic, though it should be pretty simple.

Raw light selects + raw gi * diffuse, but it produces a much brighter result for some reason, then raw lighting + raw gi * diffuse.

Let me know what you think.


raw_light_Selects_fail.zip

[Morbid Angel]

Hi Svetlozar,

Please see this additional scene attached. It uses vray fur to demonstrate the issue. Essentially when using tip opacity in the hair - once you unpremultiply then setup the render elements in nuke then premultiply back the resulting alpha looks quite different from original rgb.

Also some strange artifacting in the actual render after the unpremultiplication.

Finally the same problem with rebuilding the raw light selects - they do not = rgba.

hair_fail.zip

[svetlozar.draganov]

Hi Dmitry,

In general Raw_LightSelect Render Elements cannot match the RGB pass perfectly but this doesn't apply for Raw_GI and Raw_Lighting elements.
I did a quick comp on the first scene you send me and my composition completely matches the RGB pass(without using light-select elements).
Here is the composition: http://ftp.chaosgroup.com/support/scenes/raw_comp.zip

[Morbid Angel]

Yes, that was my point though. In theory they should match.

Also did you have a look at the second scene, with the alpha premultiplication issue?