Luma Matte Object Buffer without Matte Lines?

[Ben Hale]

Wish I had a solution for you, but I’m just writing to see if you found out a way to fix it? Could definitely use some help.

[Alex Diestel]

Hey guys.

I have had the very same problem you have now, as has everyone I know using cinema 4D. But I have just now figured the problem out.

I’m so excited. xD

The problem is this: Whem working in cinema you most likely don’t use a completely linear workflow. (check “linear workflow cinema4d” on google for this).
This means that the srgb gamma curve messes up your middle grey values, in this case the semi transparent pixels you get in your alpha channel, leaving you with a brighter or darker rim around your object.

the solution:
turn on linear workflow in cinema, create openEXR files if possible and turn the color management in your after effects on and switch to 32bit color mode if possible. the image you see should be pretty much the same as in cinema.

you now work in a linear workflow and the object channels should now fit your image perfectly.

I hope this was clear. check the numerous tuts on linear workflow out there, it’s a real lifesaver!

Alex

[Ben Hale]

I was really hoping this would help, but I’m still having the same problem. My situation is slightly different in that I have modeled a picture frame and used the object buffer to punch a hold in the middle of the frame. The object buffer is slightly smaller and giving me that white edge line when I try to composite it in After Effects. Would love to hear any theories you may have. I switched everything to Linear and it still didn’t work.

[Alex Diestel]

Hey Ben.

I seem to have been a little overenthusiastic here.
You are right, the white lining still exists even in linear workflow. I reconstructed your scene and had a go at it.
Still, I found a solution for you. The Object buffers work really well when you have an object in your scene that you want to use solely, meaning you use the white part of you matte as alpha. When you try to use it the other way round, eg “punching a hole in the frame” you use the black part and cinema/afx won’t like it.

solution:
either you have to constuct your object buffers differently, in your case that means put the object buffer on the frame, not the image and then put the frame on top of the image.
or:
use the function “matte obejct” from the compositing tag to “punch a hole” this works just fine, but will directly change your alpha instead of giving you that extra layer. which may not always be disired.

hope this helps.
Alex

[Alex Diestel]

little edit:
the trick with changing the object buffer to the other object actually doesn’t seem to work, i’m still getting white lines.
looks like the only clean way is to get it done cleanly is to use the matte obejct or even better, create the alpha in an extra shot like you would in maya. that means you copy your object, make an entirely black material on everything and an entirely white one on the part where your image belongs.
You’ll have to render it seperately, but it will be clean.

Alex

[Ben Hale]

I really appreciate you looking into it for me. I’ve been all over the internet with no success. One way I was getting it to work was by making the photo area completely green and then just using keylight in After Effects. Not the greatest work around but it was doing the trick. Problem I’m running into with that is where the green would be seen in other object’s reflections.

Do you know of a way to make an object not show up in reflections or reflect as a different color? Thanks.

[Stephen Mendenhall]

HI Ben ,
Yes the previous comment about doing a second render, giving your object a pure luminance material and everything else a material with everything turned off is a very reliable way to create an object buffer with no issues.

This would solve your problem of seeing green in the reflections. If however you like the workflow of keying out green, you could use the “exclusion” feature in the compositing tag.

[Filip Lange]

Hey Guys.

found this post, while searching a solution for this nasty little bug, once again.
since I am still working with C4D and AE from time to time i´m running in this issue, while working in linear workspace and multipass renderings.

i guess it depends on the antialiasing, and the gamma/grey interpretations…

these little white matte lines drive me creazy sometimes. especially, because its a c4d/AE problem and there is no nice fix for this, beside switching to Fusion or Nuke 😉

well, here is my workarround:
like the guy from helloluxx in the videotutorial here:
https://www.youtube.com/watch?feature=player_embedded&v=l9p5_Z0iVlg

Steps:
-setup the AE projekt in LinearWorkspace and colorspace whatever.
-interprete the mattechannels/Objectbuffers/Depthchannel with “preserve RGB” (so no changes happen to them)
-start comping. Setup the color/beautypass and place the Objectbuffer ontop. (oldschool)
-now: drop effect “set matt” to the Object buffer->create a alpha channel for the mattelayer from his own lumachannel.
-now you created a “real” alpha channel.
-you can enhance this alpha with curves and matt-choke.
In my opinion, the curves effect is more subtle and better for choking the alpha.

well.. its really a workarround and i would like to find a better soultion.. but for today it works.

cheers.

F.

[Mihai Wilson]

Seriously? I can’t believe this is still an issue considering the integration between the apps. Here’s my hack solution, make a vibrant green backdrop, give it a compositing tag and set it to compositing background. Key out the green in AE with keylight.

Sometimes I can’t believe there isnt a better way, but it works in some situations and it is fast.