Alpha gap/line on multipass / render layer

[klarwin]

Hey there!

I've been searching the forums for a while now trying to figure out a solve for this problem. I've got two passes: A beauty and a shadow. Both rendered with the same settings, each rendering a different set of layers marked with the Octane Object tag.

When I drop them in AE, I get a little line of alpha between my passes.







This doesn't happen with every render though. Some renders I've done in this sequence with the exact same models, HDRI, lighting setup, render settings, haven't had this problem. But a few have.

Any thoughts? Thanks so much!

[jayroth]

make sure that your environment color is set to black. Better yet, add in an Octane Texture Environment and set it to black. That should then allow for your alpha to be processed as expected.

[klarwin]

Thanks for the reply @jayroth

I'll give that a shot. Will it mess with my HDRI at all?

I'll report back with the results!

[jayroth]

Nope. All that does is make sure that the BG is black at render time, when those pixels are calculated. Right now, it is likely set to the default gray, which explains the color of the line you are seeing. We all run into this the first time we need a clean alpha

[klarwin]

@Jayroth

Update: Tried your fix. Still no luck. Having the exact same problem as before. As I said in my original post, the line is a line of alpha between the passes. It's not a white outline around the layer.

We all run into this the first time we need a clean alpha

Not exactly sure what you're implying here. Most people on this forum work with Octane in a professional environment every day, myself included.

[jayroth]

No implication meant. Apparently I misread your original post. My apologies.

[Samuel.fiser]

Hi ! Any solution about that problem ?
I think partial alpha of each pass multiply or add by himself and become less transparent.
I have the same issue, I tried to solve it but everytime i have white or black outline. And if i disable partial alpha, the result is unitilisable.
Even my AO pass has black outline ...
How do you do people ?

[klarwin]

@Jayroth No problem at all! Thanks for helping regardless!!

have the same issue, I tried to solve it but everytime i have white or black outline. And if i disable partial alpha, the result is unitilisable.

@Samuel.fiser So I was able to come up with a sort-of-solution.

I spent most of my EOD yesterday troubleshooting and when nothing worked, I resorted to ticking random alpha settings boxes to see if there was a magic combination. Lo and behold, ticking "Disable partial alpha" did remove the annoying outline. However, then you have the problem of the matte being incredibly jagged. My hack for that was just using the "refine hard matte" effect in AE and dialing in the settings. It's still not perfect and I have heard rendering out a separate matte for the alpha takes care of this problem. It's good enough for now though.

However, this piece is far from done and we go head-first into compositing later this week, so I'll keep you posted if we find an actual fix and not just a janky workaround!

[bepeg4d]

Hi,
have you tried with Pre-multipliy alpha option enabled?
ciao Beppe

[klarwin]

Hey there, thanks!

I did try with the Pre-Multiply alpha option on and still no use.

I'm wondering if this isn't a problem with render layers and not alpha? If I render all as one pass there's no line. But there's always a line when I render shadow and beauty separately as an Octane Multipass.