Rendering Material to alpha channel

[BBullo]

If I have a scene and I want to be able to Post-adjust a specific material in photoshop. Is there a way to save just a specific material as an alpha channel as well as the rendered image.

I want to end up with the rendered image, with an alpha channel of a certain material that I can adjust specular highlights and hue in PS.

I think this may be achived in the G-buffer output, but I don't know how to use it.

Can anyone elabotate on how you would do this?

Thanks,

[Morbid Angel]

what you are talking about is render pases, which are awailable thru vray gbuffer. However for the pases to work you need to use vray material. I doubt that you can post adjust them in photoshop, rather in combustion or after effects...however you would need to split gbuffer outputs into separete files like spec, shadow, rgb and so on. To get them going you need to switch to vray frame buffer and enable split gbuffer pases, then in gbuffer rollout clikc on which ever pases you need to be output.

[BBullo]

I don't have Combustion or After effects.
Is there no way to render just a material using a material ID with an alpha channel?; Using Max or Vray's settings?

[fgcity]

you can try to render the object (objects) with the material that you want to edit in scanline as Seperate channels. But that depends on what kind of a material it is. I don't think that you can't change something in photoshop. Any image can be manipulated. But it would be easyer if you had posted the rendered scene online and say what you want to change.

[BBullo]

Sorry I can't post the image due to a NDA. To explaine it further. I have a scene of traditional type architecture. The walls have pinstriped and decorative gold leafing on them. Some times the gold leafing gets oversaturated or blown out. I wanted to be able to separate this material "with an alpha channel?" that way I could isolate it in photoshop and use the dodge burn tool to enhance/ modify the effect.

My problem is I don't know if this is possible-rendering just a material/ or isolating it with an alpha channel through the G-buffer

[Trapezium]

I did a few tests with VRay. The Material ID G-Buffer in VRay should work for what you want to do but it doesn't appear to be functioning currently.

There may be a work around though you'll have to convert to standard materials in a temporary file to create a selection to use in Photoshop.

Switch to Scanline

Convert materials to Standard

Set the material you want to edited to a specific Material Effects Channel in the Material Editor (lets say we set it to "3"). It's the 5th button from the right that is set to "0" by default. This needs to be different than all other materials.

Add the Matte Render Element in the Render Scene Dialogue

Check Effect ID at the bottom

Set the value to correspond with the Material Effects Channel that you've set for your material "3".

Hit render

Hope this all makes sense, Some of the terms are different but actually refer to the same concept. I've tried to write what the fields say rather than use the same term throughout. So basically...

Effect ID= Material Effects Channel= Material ID (VRay)

Once you get this black and white image you can use it as a selection in Photoshop. You should probably try to match the AA as close as you can.

Let me know if it works for you, I'm not sure how complex your scene is but it worked on a simple mockup I made for testing.

--Jon