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Rendering with Arnold in Houdini and Solaris using the HtoA plug-in.
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HtoA, how can I render the beauty with Alpha and have the Skydome HDRI appear into the background AoV at the same time?

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Message 1 of 4
giandosopaolo
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HtoA, how can I render the beauty with Alpha and have the Skydome HDRI appear into the background AoV at the same time?

Hi

I have a scene in Houdini with a HDRI plugged in a skydome arnold light.

In the Contributions panel the Camera Rays are set to 0, all the other rays are set to 1.

For this light "Skydome Indirect Lighting" is disabled.

Then I have a blurred version of the same HDRI plugged in a second skydome arnold light.

In the Contributions panel the Camera Rays are set to 1, all the other rays are are set to 0.

For this second light "Skydome Indirect Lighting" is enabled.

This way the blurred HDRI is saved in my Background AoV and not in the Emission AoV.

My problem is that I would like to render my beauty with the alpha channel, and I can not figure out a way to enable it and keep the background AoV.

If I disable "Skydome Indirect Lighting" for the second light I obtain my RGBA beauty but I loose the Background AoV.

Any suggestion or workaround?

Thanks

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3 REPLIES 3
Message 2 of 4
Anonymous
in reply to: giandosopaolo

it's a bit of a headache but it's works!
1- add the same attribcreate to all your object:
- name: Mask (or what ever you want)
- Class:primitive
- Type:Float
- Size:4
- Default & Value:1
2- Use user_data_rgba & aov_write_rgba with the same name: Mask
standard_surface ==> aov_write_rgba.passthrough
user_data_rgba ==> aov_write_rgba.aov_input
aov_write_rgba ==> OUT_material

3- add Arnold Aovs, name it Mask
4- Render: you end-up with beauty and Mask
5- use copy channel in Nuke to copy the mask channel to rgba.alpha
skydome.jpg

Message 3 of 4
giandosopaolo
in reply to: Anonymous

Thanks @Rachid!

Just a clarification:

Must I create this user_data_rgba & aov_write_rgba==> OUT_material just once or must this be done for every standard_surface material in my scene? Meaning, every material before connecting to its OUT_Material must have its very own aov_write_rgba?

Many Thanks

Message 4 of 4
Anonymous
in reply to: giandosopaolo

Just once, otherwise you end up with a lot of unnecessary alpha, if you do it for each shader!
what you can do is assign one standard surface to all your objects and make a custom aov with the same setup user_data_rgba & aov_write_rgba

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