pRef or Preference Passes

[Nexus Productions]

I'm trying to get some information about rendering a Preference or pRef pass that our comp lead needs.

The way it's been described to me is its like a Pworld pass but the color information is in vertex local space, so that the color value tracks the point on the geometry. this video talks about it and demonstrates the technique at 07:08

https://vimeo.com/18701863

It is also mentioned here in this forum post:

http://forums.cgsociety.org/showthread.php?t=1056819

Although this cites Maya we tried the VraySamplerInfoTex node as an VrayExtraTexture pass in vray for 3dsmax. Following Vlado's advice I tried rendering some tests but it doesn't yield the correct information.

Point > Object
Point > Camera
Point > ReferenceObject > Sphere attached to one of the deformaing meshes
Point > ReferenceObject > cached geo object
Point > ReferenceObject > predeformed cached geo object

This is me just trying random stuff in the absence of any documentation on this texture node, so I didn't have any real hope I'd see the results we were looking for.

The only infomation I can find on vray pertains to vray for Nuke, which has a "PointObject" option. We don't have vray for nuke yet to try this.

http://docs.chaosgroup.com/display/VFN/VRaySamplerInfo

If i'ts something I need to try in Maya as the setup I can try this too.

Any suggestions? None of our lighters are sure what to do either.

cheers,

Pete

[joconnell]

You can choose a reference object in the sampler info pass for position passes - if you choose the pivot of an object or even some kind of null then that'll become the centre of where the coordinates are drawn from. That'll let your comper use the pselection gizmos in nuke and have a soft selection travel with an object through a render.

As for vertex coordinates on a mesh that deforms, your only option here is using a uv pass and then using the stmap filter with your uv passes to have some kind of drawn matte travel with your object - it'll stick to it perfectly so you can use it for grading animated characters and what not. The only bad thing is you can sometimes get slightly pixelated edges since uv passes can only have one value per pixel.

[vlado]

The pRef pass in 3ds Max can be done by baking the initial vertex positions into a map channel (f.e. using a UVWMap modifier in "XYZ to UVW" mode) and then using an ExtraTex render element with a VertexColor map to extract that channel into a render element.

Best regards,
Vlado

[joconnell]

Well that shows me, doesn't it

More handy tricks!

[Nexus Productions]

Vlado, that's perfect. Thank you for your answer.

and Jo, thanks for chiming in - the compers mentioned your approach is just as valid but the vertex color way is quick to setup. One thing we noticed, we needed to set the UVWmap modifier to the vertex color channel so we didn't interfere with the mapping on other AOVs.

cheers!

Pete

[joconnell]

All good pete - we've ken hau in here at the minute and wesley roblett has been over too - congrats on the great work on the slack ad! Everyone I've known that've gone through nexus say it's a lovely place to work.

[Nexus Productions]

Thanks Jo,

That's kind of you to say. We have Wes here at the moment and he was the one who asked me to look into this! Please say hi to Ken for me.

Pete