Alpha Gain parameter not working with Arnold

[litote]

I am rendering sprite particles in Arnold and am trying to adjust the alpha of the particle image I used to make the sprite more transparent. In Hardware Render 2.0 you can do this by adding the "alpha map" (I am using a PNG) to the Transparency field an adjusting Color Balance-Alpha Gain parameter that is below it.

But If I use an aiStandard material for rendering in Arnold and put the alpha map in the Refraction-Opacity parameter to create the alpha transparency, I find the Alpha Gain has no effect on adjusting it as it does with Maya Hardware 2.0 renderer.

Is there a way?

[mspeer]

Hi!

I am a bit confused by your explanation, but for Opacity in Arnold in general:

1. Shape node, Arnold tab disable Opaque

2. In Arnold material use Geometry -> Opacity

[litote]

Geometry -> Opacity? Do you mean Refraction-Opacity?

[mspeer]

Hi!

No. Tab Geometry, then Attribute Opacity.

[litote]

Tab Geometry? Where exactly?

[mspeer]

Hi!

In Arnold material like aiStandardSurface.

[litote]

I see no "Geometry" tab in the aiShader. I see only rollouts... Matte, Diffuse, Specular etc. The only Opacity parameter I see is in the Refraction rollout. Where are you seeing it exactly?

[mspeer]

Hi!

It looks like you are still using Arnold 4 which doesn't have aiStandardSurface material.

So Opacity is to be found at an other place. (i can't test this anymore)

Please read the Arnold for Maya User Guide for more details.

[litote]

I upgraded to Arnold 5. The same control ha no effect either.

[mspeer]

Hi!

Please upload the scene-file + texture(s) for particles.

[litote]

Hello,

I have attached the scene as a zip file. It includes the texture file.

The Color Balance-Alpha Gain and Alpha Offset attributes in the Geometry-Opacity parameters where I added the alpha map (click on arrow next to Opacity slider in the aiStandardSurface shader tab) have no effect. They did work with Maya's Mental Ray and Hardware 2.0 renderers, but not for the aiStandardSurface shader in Arnold 5.0.0.2 (MtoA 2.0.0.1).

[mspeer]

Hi!

Alpha Gain only affects Alpha Out, but you are using Color Out.

Check in Node Editor or Hypershade.

[litote]

Hello,

What connection do I need to alter in the node graph? I have attached the screenshot of the current graph.

Thanks

[mspeer]

Hi!

Out Color+ ----------->------------ +Opacity

[litote]

Did you look at the image of the node setup I attached? Is it correct? I have the map I added to the Geometry-Opacity field linked from Out Color to Opacity but the Alpha Offset has no affect.

[Stephen.Blair · Accepted solution]

Alpha Gain and Alpha Offset apply to the alpha value output by the MayaFile node.

[mspeer · Accepted solution]

Hi!

"from Out Color to Opacity but the Alpha Offset has no affect"

Correct, Alpha Offset has no effect on Out Color.

Alpha Offset has only effect on Out Alpha.

So use Out Alpha.

[litote]

Thanks for taking the time to post this screenshot Stephen. I couldn't get the output to connect to the Opacity as I didn't realize you had to twirl it open and connect to the RG and B. Presumably you use the Alpha Gain in the Color Balance rollout to adjust the alpha?