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Arnold AO shader causing black lines on seams

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Message 1 of 7
litote
3584 Views, 6 Replies

Arnold AO shader causing black lines on seams

I used this method to create a texture from AO:

 

Add a aiArnoldAmbientOcclusion (Arnold-Shader) shader to the mesh.
Select the mesh and go to Arnold menu-Utilities-Render Selection to Texture. In popup set a Resolution and the directory. Hit Render button (it will render as .exr with name taken from mesh).

 

However, when I add the texture to a shader it shows black lines along the UV seams. On post suggested to unpremultiply the image. If this is the way, how does one do it?

 

Any other suggestions?

6 REPLIES 6
Message 2 of 7
sean.heasley
in reply to: litote

Hi @litote

 

There's a quick read on premultiplied images you can read here.

 

I'm not completely convinced that's causing your issue so when you get a chance, can you please zip and attach the scene file here or via dropbox/google drive or another file sharing program so I can take a look at it?

 

Let me know if anything changes!

Message 3 of 7
NandoStille
in reply to: litote

Did a quick test. Gosh, who wrote this tool? I can't believe there is no option to deal with texture borders!?

Back to school! See "Fill texture seams" here: http://knowledge.autodesk.com/support/maya/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/Maya/file...

 

Now for a solution: unsurprisingly the relatively new "unpremultiply" shading node doesn't work, but we don't need it anyway.

What we want to do is to divide RGB of the baked texture by the Alpha of the baked texture, which is called "unpremultiply".

 

So, just use a multiplyDivide node, switch it to "Divide" and connect it like this:

 

unpremultiply.png

 

 

 

Message 4 of 7
mspeer
in reply to: NandoStille

Hi!

 

The node "unpremultiply" is currently not supported by Arnold.

https://support.solidangle.com/display/A5AFMUG/Maya+Shaders

Message 5 of 7
litote
in reply to: NandoStille

@NandoStille

 

Great solution! Thanks, saves me messing about in AE.

Message 6 of 7
NandoStille
in reply to: mspeer


@mspeer wrote:

Hi!

 

The node "unpremultiply" is currently not supported by Arnold.

https://support.solidangle.com/display/A5AFMUG/Maya+Shaders


Yes, thought so, did not check the log.

 

The lookdevKit nodes lead a quite unnoticed (maybe neglected) existence. Badly supported by 3rd party renderers from the beginning which was in 2016 I think. Is any Renderer supporting them? Oops, getting off-topic.

Message 7 of 7
litote
in reply to: sean.heasley

@sean.heasley

 

Hello Sean,

 

Someone posted the solution.

 

My scene was very simple: All I used was a cylinder primitive and added the aiArnoldAmbientOcclusion shader. Then rendered it as a texture map from Arnold menu-Utilities-Render Selection to Texture. Then plugged the texture into the Base Color of an aiStandardSurface shader. It renders/premultiplies with the black seams. But the MultiplyDivide node in the solution give in this thread fixes it. Apparently the unpremultiply node does not work.

 

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