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Why has this Z depth expression not yet been made?

Apr 17, 2012 10:44 AM

I recently had an issue where I needed to composite two objects from a 3d application together on separate layers..  But the objects interact in such a way where sometimes an object from layer A is in front, and sometimes the object from layer B is in front.....  But the layer order would give me a result where either A or B is in front the whole time depending which layer is on top in After effects.



(Yes I know in that example you could simply mask it, but in reality there were several objects all dealing with the issue named, and it would have been too complicated to do so.)





So in my search for the answer I found this tutorial...



This is a good answer if you're only dealing with two layers...  But it doesn't have an answer if you're dealing with any amount of layers more then two..... 



Soooo here's my question, why has nobody made a script, option, or button in After Effects yet that simply says "do you want to use the Z depth in your RPF/RLA file to determine where the objects should fit in the scene???"



I ask only because it seems like the most obvious thing to do.  If the 3-d application went through the trouble to create the option to have Z depth information, and even has file types that support having that information, then why wouldn't the compositing program have an option to use the information in the most obvious way?

  • Currently Being Moderated
    Apr 17, 2012 10:58 AM   in reply to gabeartist01

    It's not obvious, it's complex. Z-buffer data bears no relation to physical depth and unless you give a baseleine reference, it's useless. Furthermore by no means must such data be linear, depending on how the 3D program creating it treats "depth" in its camera system. And where it falls most obviously apart - except for sampleImage() there is no way to access pixel data. Since that would need to be done in loops and on multiple layers, it would be slow as hog. So despite your assertions, this is far from simple or trivial in many ways and for performance reasons alone best left to plug-ins liek Buena Depth Cue or andsy of your facorite Z buffer tools/ DOF blur tools where the user simply can pick a desired depth plane with a color picker or crosshair and the code does all the hard work.



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    Apr 18, 2012 12:26 AM   in reply to gabeartist01

    Yes, it's a Pixelbender plug-in, which is a whole different thing than expressions, which is what you asked about...



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    Apr 19, 2012 8:33 AM   in reply to gabeartist01

    Hey Petterson's to set up your render passes in a more efficient way. Rendering out a separate alpha for each object that takes into account the other objects in the seen is easy in most 3-D applications. That will solve your crossing problem.

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