Render Elements_masks for materials

[max montana]

hi,
i work on my first project with vray and can`t manage it to get masks for specified materials in the scene with the render elements.
in viz/max i give a material a mat-id in the mat.editor, then define the same mat-id in matte in the render elements, and get a perfect antialiased mask of the objects with the defined material. i use this for comp in photoshop.
when i try this with vray i get no alpha channels, but a non antialiased g-buffer, with no possibility of getting masks of the materials with the defined mat-id`s.
i guess this is a very basic problem, but although i searched the forum for 2 hours i found nothing that solved my problem. if this probl. has been bespoken yet, please give me the link.
thanks

[instinct]

The best to get proper masks is using MultiMatteRenderElement. Then set it to "Material ID" and specify the IDs you want/need.

You get 3 masks per MultiMatte and they are in the RGB channels. This way you get perfect masks rather then flaky color-selecting that is never pixelperfect.

Regards,
Thorsten

[trick]

The best to get proper masks is using MultiMatteRenderElement. ...

Keep in mind that this does not support opacity maps !

[thablanch]

Turn all to pure standard mats black self illum, except the mat you need, white self illum, then the selection is perfect. Alpha is still in there as well.

[trick]

Turn all to pure standard mats black self illum, except the mat you need, white self illum, then the selection is perfect. Alpha is still in there as well.

Then RenderMask is much easier

[Pixelab]

Yeah, but IMO VRayWireColor do a wonderful job 90% of times for just one click. You just have to keep attention in your objects color and the only drawback is de multisubobjects that renders the same color.

But... it works perfectly with masks.

For really "pixelperfect" precise masking, MultiMatteRenderElement is your friend... I'm not a big fan of the "self illum" technique which requires a second rendering.

[instinct]

Well if you have to combine several layers into one rendering you have to use pixel perfect masks or the AA will give you dark or bright edges around the layers.

Kind Regards,
Thorsten

[max montana]

wow 6 replies in half a day, i am really impressed about the cooperativeness in this forum, thank you very much.
i will find some time tomorrow to give your suggestions a try, and will post progress(if i make one...)

[max montana]

after initial difficulties i managed it to get the masks for specified materials with multimatte render elements.
my workflow:
i give different mad id`s to the materials, then define the first multimatte render element for the first material. i check "vray vfb", "r gbuf id" and define the mat id number for 1 material, and at least i check "mad id". material. can someone tell me what the g gbuf id and the b gbuf id are for?

i also tried to get a .exr file where all masks shold be enbedded, but didn`t make it until now. i wrote out a vray raw image and manually changed the ending to .exr, also tried it with save seperate render channels, but alsways get a tiny exr. file with only the rendering in it.

[instinct]

What are you using the view the EXRs ? PS for example doesnt support multichannel EXRs out of the box. r gbuf is the red channel, g the green and b the blue channel. As they are saved as independent channels you can get up to 3 pixel perfect masks for each MMRE.

Regards,
Thorsten

[max montana]

which programm will i need to watch the exr? but anyway, it would not make much sense for me to make a exr, as do post in ps.
so i will save the mmre`s by hand, open the files and dragand drop the channels to my rendering.
better workflow possible?

[instinct]

Well there is a Multichannel import plugin for PS, but i never tried it as we never use PS for post so i cant comment on that one. We use nuke and it's EXR support is still unsurpased. No other tool offers the same flexibility for EXRs currently.

Regards,
Thorsten