Crunchy white outline on alphas? / C4D

[TommyTronic 0]

I'm getting this crunchy white outline on my alpha when rendering out of Cinema... Anybody dealt with this before? I can't figure out why this is happening.

 

 

https://www.dropbox.com/s/ibp26yt5bq8ulb7/Screen%20shot%202014-03-02%20at%208.19.20%20PM.png

 

Tommy

[vozzz 2]

is it straight alpha?

[TommyTronic 0]

Yep, straight alpha.

[TommyTronic 0]

Such a pain for my compositor! I gotta fix this, I'd be annoyed if I were him too!

[TommyTronic 0]

I wanted to add, that these tentacle looking things are a hair material on a tracer, so I'm guessing because it's hair is the reason it's not rendering with an object buffer... The type is fine, but I need a clean alpha for these hairs.

[vozzz 2]

straight alpha always renders crunchy. then when you apply the alpha it should all be nice and smooth.

 

its called "premultiplied" in AE i think.

 

im pretty sure its just a matter of changing the alpha settings in AE.

[rich 0]

Yes set your input to "straight" alpha mode on import in AE. Normally its used to stop you getting black fringing on your renders - so its essentially a better way to render out, although after effects is good at removing the black fringe if you import as "premultiplied"

[TommyTronic 0]

Yeah, it's being interpreted upon bringing in to AE as straight, and we've tried it premultiplied too... Neither works. What am I missing?

[sbmotiondesign 0]

When it comes to cleaning up edges and removing fringe I've had good luck with the min/max effect in AE. It basically expands and grows edges based on color. That when used in combination with the set channels effect might be able to get you a clean result?

 

EDIT:

Looking again at your image, you have anti-aliasing turned on in C4D right?

Edited March 4, 2014 by sbmotiondesign

[TommyTronic 0]

Thanks. I'll try out that effect.. I'm using the physical renderer and the anti aliasing settings are different there... I'm not too familiar with the physical renderer. Here's a screenshot. I've got it set to Mitchell.

 

https://www.dropbox.com/s/e2iox2nfp3cl3j8/Screen%20shot%202014-03-04%20at%205.35.53%20PM.png

[TommyTronic 0]

This is way too simple a thing to be having so much trouble with... sheesh.

[AromaKat 1]

Can you post your scene file as-is?

[TommyTronic 0]

It's at the office... I will tomorrow. I figured out the problem though. Did you still wanna see it?

[AromaKat 1]

What was the problem?

[TommyTronic 0]

I had straight alpha checked in render settings... I'm used to rendering straight alphas out of AE, but apparently this is not what you wanna do in Cinema... Unchecked straight alpha and it worked perfect.

[AromaKat 1]

straight alpha is correct. Premultiplied can give you problems.

 

I suspect this compositor person you referenced needs to interpret alpha as straight. Then all will be fine.

[TommyTronic 0]

I'm tellin ya, that isn't working... Tried several times. And straight alpha was what I knew was right, but I swear in this case, straight alpha was the one giving me problems. Soon as I checked it off, alpha was fine... I dunno man. Weird.

[TommyTronic 0]

I do want you to look at the scene file though, cause everybody has told me the same as you... So when I get to the office in the morning I'll post the scene file if you don't mind taking a look at it.

[AromaKat 1]

Okay. Whats being used to composite?

[TommyTronic 0]

AE creative cloud

[jayfaker 1]

I've had the same problem before. I had guessed that C4D was just screwy and the straight vs. premultiplied settings were reversed or something. If I unchecked straight and then interpreted it as straight in AE it worked just fine. I dunno, maybe there is something I was missing.

[Davor 0]

It appears that you have a "Background" object in your scene with a grad on as a material. I think that's throwing the alpha off in calculating the proper straight matte. Maybe try hiding the background object and see what kind of result you get.

 

Side by side of my experiment: (1st with background object active, 2nd with out)

[anothername 0]

I've had the same problem before. I had guessed that C4D was just screwy and the straight vs. premultiplied settings were reversed or something. If I unchecked straight and then interpreted it as straight in AE it worked just fine. I dunno, maybe there is something I was missing.

 

This happens to me all the time and I use the same workaround, always wondered if there was a proper explanation of what's going on here...

[Smuzzler 0]

Also just make sure how your rendering it out that the codec or file fomate supports alpha channels.

[AromaKat 1]

Can you post the file? I have never had this issue, and whats being described sounds like the kind of problems premultiplied gives me - not the other way around.