Nesting Layers & Black Edges in Combustion.

[sindbad17]

i see on the screenshots in your post that one or many layers have an Add transfer mode.
That's the reason why you get black edges in the blured parts of your layers, where the alpha is not at 255. When you nest these layers, they don't blend anymore with your white background but on a black background, so you get those black edges.

Always remember that nesting layers with blending modes changes the way they react.

So maybe you should instance your bg, nest it with the layers you previously wanted to nest and on that comp, apply a Compound Alpha Arithmetic, and use the alpha channel of the pass containing the matte of the whole 3d object you rendered ( aka not the specular but the diffuse pass for example ).

I hope it will solve your problem and good luck


Fabrice
---/Combustion-After Effects-XSI/---

[thatoneguy]

I actually don't think this is an issue of pre-multiplying... well... I guess technically it is, but it's not because of your render.

If all of your layers aren't set to "normal" on their transfer mode, which I expect they're not since you rendered in passes, they aren't going to be lightening, dodging, multiplying or any of those goodies that they would do to the background if they had a piece of background footage behind them to effect. If you have a layer set to "lighten" and it has a black background, it's just going to be normally opaque" This really is the black eye of layer based compositing, although technically you should be able to do your composites without multiply, screen or dodge transfer modes. You might want to look into how to do that, and that's how you would probably do it in shake or fusion. (You would also have this problem if you used Shake's multi-layer node. Or in photoshop if you grouped a bunch of layers.)

Or who knows... maybe this isn't your problem, but hell here is how to do nested 'photoshop' layer transfer modes.

A workaround would be, if you really want those objects grouped, but mind you this could very messy very fast, and is innefficient. Go into your schematic viewer:

Mid-type Edit:

This thing is behemoth, here's a link, I'm not going to try to do a step by step, it would be too long and too confusing:

http://vaporware.w3dzine.net/Swap/screening_background.cws

Feel free to ask questions onhow it works. ;)

In short, what I did was take the alpha of the foreground elements, take the "max" of their unmultiplied alpha alpha channels and then mask a copy of the background to move around with them inside of their composite. You will also notice you have to be careful to wire the Foreground Level below you's composite into your background or else, you'll have a solid overlap of an un modified background in order to stack.

However, by the time you've gone through all this, you really aren't seeing any sort of benefit over just keeping it all in one Composite. In fact there are endless reasons why you shouldn't. So I would recommend look at how it's done, see if there is anything you can learn, and then just don't nest the layers. Especially once you have more than one foreground element. At that point you're going to be looking at overlapping issues. If the two foreground composites overlap, wherever the opacity is supposed to be 50% it'll be 100 and it won't look right at all.


*whew* Best of luck.

[lazzhar]

Thanks guys really appreciated.

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