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Rendering with Arnold in CINEMA 4D using the C4DtoA plug-in.
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Alpha Fringe

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Message 1 of 9
mphillips0007
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Alpha Fringe

I am trying to add a logo to an object and using Alpha stacking. I am getting a black fringe around my shader. Is this the preferred way of working with Alphas? How do I remove the fringe ?screen-shot-2021-04-16-at-20258-pm.pngalpha.jpg

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8 REPLIES 8
Message 2 of 9
daniel
in reply to: mphillips0007

Looks like a premultiply issue to me.

Message 3 of 9

Where do I adjust the premultiply setting?


Message 4 of 9

The workflow is similar how stacking works natively. Assign your materials in order (base, layer1, layer2, etc.) and setup the alpha on the top layers.

Alternatively you can define mixing within one Arnold material via the mix or layer shader, for instance:

mix-shader.png

Not sure where the black fringe is coming from. The alpha channel looks correct, right? Can you send me the texture to take a look?

Message 5 of 9

Peter, thank you for your answer. I should be more clear and I apologize this could be my lack of knowledge(Probably is). I am applying labels to objects. My logos are created in Photoshop and saved as a PNG with a transparent background. Could I be doing something wrong with saving the PNG in Photoshop? I have a base texture in this example, a standard surface with a white color and then I have my label as another texture so I can control placement of the logo and scale separately(See Below).

Would I just connect the PNG to standard surface shader color and image alpha to Main Geometry Cutout Opacity to cut out the logo? Unfortunately, this still has a fringe with this method. What is the point of Alpha Stacking method? It seems to yield same results but a lot easier? Again, thank you for your time and knowledge. screen-shot-2021-04-20-at-115726-am.png

Message 6 of 9

Probably in this case cutout opacity and alpha stacking produce the same result, but they are slightly different methods, so that's not always the case. For instance if you have multiple layers, you cannot use cutout opacity. In general, stacking or layering is a more natural workflow when adding a logo to an object.

Back to your question, not sure what's wrong. You can check the alpha channel if you turn on Single channel in the image shader and set the Start channel to 3. You can also try to save a tif or exr from photoshop.

Message 7 of 9

And of course you can send me the scene or send it to support@arnoldrenderer.com, and I will take a deeper look.

Message 8 of 9
Anonymous
in reply to: mphillips0007

Any update on the alpha channel fringe? I'm running into the same problem when doing a simple .png label saved out of Photoshop. Can't seem to find anywhere to change the premultiply settings and both methods of alpha stacking are producing the same result.


The only workaround I've found is to produce separate color and alpha images with the color bleeding all the way to the edge of the image in the same way a straight alpha image looks before being multiplied. It works but would be more convenient if a standard Photoshop .png with transparency worked the same way it does with other renderers. For reference, other formats that support transparency render the same way, including tif.

Message 9 of 9
peter.horvath6V6K3
in reply to: Anonymous

No progress on this, I'm afraid. I see that it makes the workflow very inconvenient, I'll try to push for it in one of the next releases, but I can't promise anything.

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