I’m trying to render an image with an accurate alpha channel so I can add a background image in photoshop later.

I am using Max 9 + Vray 1.50.  I am getting my alpha channel to come out in my tiff file but it is completely opaque for all the objects??  I have a glazing material that has reflections on it and also a window blind that is semi-transparent.  How do I output or make an image so the alpha channels shows these characteristics.  Thanks in advance for any help.

Regards Peter.

I would start by posting in a VRay forum.  This one is for Autodesk VIZ.

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— Image Technologies --
Modeling, Rendering Animation
http://www.imagetecmra.com
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Yep - did that and no response - I don’t think it is really a Vray issue though.  How do you save out an alpha channel with those characteristics in Max/VIZ???  It should be the same??  The output render area is on the common tab which does not change when using Vray/default/Maxwell or VUE renderers.  Thanks.

Regards Peter.

It may have to do with the type of file you render to.  Not all file formats contain alpha info. 

I always render to TIFF or TGA.  Then in Photoshop you can select the alpha channel.

Have you tried that?

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— Image Technologies --
Modeling, Rendering Animation
http://www.imagetecmra.com
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Personally, I don’t use Viz or VRay, but check the opacity or refraction of the material to ensure it is affecting the alpha.

Calvin Clayton, Jr.

Yes - I have tried both and I do get an alpha channel but it just doesn’t seem to include any semi transparent or reflective materials in the alpha channel.  It gives me just a completely opaques selection.  What I want is to slip a background image behind the semi transparent - window blind and window reflections.  Here is the image and the alpha I get.  Notice the window blinds and reflections on the windows that aren’t represented in the alpha.  Thanks for the reply.

Cheers Peter.

Thanks Calvin - Yeah I have already done that.  Like I said, I don’t think it is a vray problem. See my post above and view the image.  I can’t seem to get a semi transparent material to show up in the alpha channel.  It is either completely transparent, like the window glazing, which should have the reflection in it as semi transparent, or completely opaque, like the blinds which should also be semi transparent.  Thanks again.

Regards Peter.

Is there some reason why you can’t use your background pictures as the background in MAX?  Just have MAX render it all together?

I’m not sure you can do what you want without some advanced compositing software…

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— Image Technologies --
Modeling, Rendering Animation
http://www.imagetecmra.com
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I will give that a try.  That may be more of a Vray question because there is a vraysky map in the environment slot.  I think that I can place it in the viewport background but how would I have it render ?  Can you do that in VIZ?  Is there a place to render the background without putting it in the environment slot?  Thanks.

Regards Peter.

Nope.  That’s how you do it in VIZ - same as MAX.  Environment slot.

VRAY is probably like Mental Ray in that it takes over the environment setting....  You’ll have to check with the VRAY people to see if you can over-ride that.

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— Image Technologies --
Modeling, Rendering Animation
http://www.imagetecmra.com
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Maps in the environment slot suck.  Don’t do it.  Build a piece of geometry outside and apply the map in a material.  Self illuminate it, or use the Architectural material and set it to Raw Diffuse.  Works like a charm, is easy to adjust, and will save you time. 

As far as your alpha problem, what is the difference between your glass material and the blinds?  Obviously, the glass is properly affecting the alpha, but the blinds aren’t.  What type of material are you using for each?  If you are using VRayMtl, make sure that Affect Alpha is checked.  And reflections in the glass won’t affect the alpha channel.  They are not a change in opacity, they are just part of an image applied to the glass object.

Chris

3DS Max Design 2011 64-bit - Advantage Pack
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