Alpha channel in OpenEXR not working during render time

[nver009]

Hi,

I have problems with rendering OpenEXR RGBA Float. The problem is that the alpha channel will not come through (Which I checked with Nuke). In the viewport renderer using 'Q' + Drag it was definitely clear that there was an alpha channel when I flipped it to Alpha. The material I used is mia_material_x (Glass shader) plugging only the 'reflection_result' into Surface of the Shading Group which recieves reflections from HDRI. The only light source is a HDRI.

What would the problem be?

[Kzin]

Hi,

I have problems with rendering OpenEXR RGBA Float. The problem is that the alpha channel will not come through (Which I checked with Nuke). In the viewport renderer using 'Q' + Drag it was definitely clear that there was an alpha channel when I flipped it to Alpha. The material I used is mia_material_x (Glass shader) plugging only the 'reflection_result' into Surface of the Shading Group which recieves reflections from HDRI. The only light source is a HDRI.

What would the problem be?

you have to check the alpha option in mia mat:
"transparency uses background alpha channel"; its under additionell options.

[nver009]

Thank you for the reply!

However I cannot find that switch to turn on "transparency uses background alpha channel" in the mia_material_x. Can you please show me an example?

Thank you!

[ActionArt]

Sorry to ask the obvious, but are you saving the exr as RGBA, not RGB?

[Hirazi Blue]

Thank you for the reply!

However I cannot find that switch to turn on "transparency uses background alpha channel" in the mia_material_x. Can you please show me an example?

Thank you!

With the different naming convention between the Architectural Material and the mia_material I believe you'd have to look for the "propagate_alpha" parameter...

[krazeban]

Hi, I'm working with nver and replying for the group.

Yes it is set to RGBA. I have tried both TIFF/RGBA/Float, also OpenEXR/RGBA/Float. Both yielding the same result.

I have also tried the 'Propogate Alpha' switch located in the mia_material_x but with no success. Could it possibly be a problem with the HDRI?
The way I created it is by Edit->Current Pass->Pass Shaders->Environment. I hook up the HDRI to Environment and turn the 'Background' attribute to 0 to get only the Reflections which is what we require.

This is some WIP videos to what we're doing which is simply a glass shader using mia_material_x reflecting a HDRI. They were batch rendered but the problem is that they have no proper alpha that could be worked with in Comp.
https://vimeo.com/53292274
https://vimeo.com/52989925

Thank you for your help

Ba An

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