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comping 3d images with gamma 1.0 results in alphas with black borders.
Hi!
I am a 3d artist that relays quite heavily on different render passes. Comping them together in after effects is usually not a problem. After all of my operations is done I simply put an alpha layer on top of my comp, that removes any sign of black borders and anti aliasing problems.
However when working with gamma 1.0 in my 3d package this method doesn’t seem to work. I am left with a black border in my precomps anyway. Do I have to do anything to the alpha of my 3d images before I do any comp operations? Some Nuke guys I know told me there was a checkbox or something that did something to the alpha. Sorry if I am vague. I will post some images soon to illustrate my problems.
My basic question is. How do I remove black borders from my precomps when comping 3d images rendered with gamma 1.0 settings?
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16 Replies
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I might have found something that actually works. If you add a levels effect on the layers using some blending operations (add, mult…) then apply a value of 0.45 on the alpha. The black halo around the object is gone. I believe I have de-gamma the alpha. Not entirely confident on the linear workflow stuff. Just trying to find something that works.
I think Adobe should give the color space in AE some attention. This issue isn’t one in the other compositing tools.
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I use V-Ray as my renderer of choice. It doesn’t support straight alpha output. If it did I believe this wouldn’t be a problem
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Did you let AE know that the footage was premultiplied? Unless V-Ray was applying different gamma to the alpha than the RGB (which would show up as a problem in any compositing pipeline) I can’t see why the standard un-premultiply wouldn’t work.
If you’re using the EXtractoR plug-in you should note that the color and alpha settings you choose for the footage items in AE’s project panel will be ignored on instances of the footage with EXtractoR applied. The plug-in reads the data as-is from the file. If you want to un-premultiply an image using EXtractoR you check the “Unmult” box in “Process” section of the effect.
Darby Edelen
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Forgot to mention, part of the color settings that you have to worry about when using EXtractoR is the linear color. If your working space is not linearized then the extracted color will look dark. I doubt that’s the issue as you would’ve noticed colors being off, but I thought I should mention it. If it is a problem then either linearize the working space (because: why wouldn’t you?) or use a Utility > Color Profile Converter effect to convert to linear.
Darby Edelen
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Hi Darby!
Thanks for the info. I do believe that my footage is linear. And I do get black borders. My footage is set to premultiply and my project settings are linear. I have some issues with real time playback when using linearize working space(RAM preview). That is why I prefer to leave it off and use “match colors using 1.0 gamma” instead.
If it’s not to much trouble could I send over a ae file and maybe you can have a look at it. You seem to know what you are talking about.
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[daniel tegeland] “If it’s not to much trouble could I send over a ae file and maybe you can have a look at it. You seem to know what you are talking about.”
Sure, no guarantees there’ll be a solution but I can take a look. If it’s a relatively small file you can upload to the COW otherwise you can use dropbox or something like that.
Darby Edelen
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Thumbs up!
Here is a test scene I did to illustrate the problem. I did a comp of the render elements. Using them results in bad anti aliasing. The problem multiplies with the number of layers used. Maybe this isn’t a gamma problem but the fact that I m using pre-multiplied images? Just want a workflow that doesn’t produce this problem.
The zip contains an aftereffects scene, exr images and a max scene. I didn’t include the hdri used in the scene.
It would be great to hear your input in the matter.
below is the link.
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So it is definitely related to the premultiplied images and the way that AE handles compositing.
This may seem counter intuitive but what you’ll want to do is composite all of your layers against black. Then use a copy of the footage at the top of the stack set to the Stencil Alpha blend mode to punch out the alpha from the lower layers.
You shouldn’t need to do this if you’re compositing onto a background directly, but if you need to render out again with alpha (or there’s an intermediate step where you need good RGBA values) then you’ll need to do the above.
Here’s an example file using the assets you provided:
Darby Edelen
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Hi Darby!
I does seems that this does the trick in this particular scene. I imported some more objects and change the lighting some and all of the sudden I have the same problem again, although I just replaced the images from your comp. Strange. If you can find it in your heart to look at the same setup once more with a different rendering I’d be appreciative. It’s pretty close now though, but it would be nice to always know I’d be dead on.
6967_testedgefixedconvertedfolder.zip
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I’m running CS6 so I can’t see how your compositions are set up. I was able to get the same result with the new assets you uploaded though.
I did notice that the results look worse when using Blend Colors Using 1.0 Gamma only. I linearized the working space in the project files I’m working in and everything looks good.
Darby Edelen
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