Zdepth Opacity

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  03 March 2005
Zdepth Opacity

I am wondering if there is a way to do a Z-depth pass with opacity maps. We currently use RPC people for interior renderings which, for those who don't know, are just a plane with an image and an opacity map.

I am using the zdepth pass into photoshop with a lens blur trick, but with RPC it screws evertything up. Instead of an outline of a person, I get a big box.

Can anybody help me?
  03 March 2005
this is from a similar post on the Discreet Site -

Quote: well, it's a problem of 3dsmax. if you render out z-depth and i think that's what you did, 3dsmax does not regognize opacity. so of you have some mapped planes in your scene,say with a tree image mapped on it, not the shape of the tree is visible in the z-depth image but the shape of the plane. i hope discreet works this out.

the workaound is to render a special z-depth scene pass. give all your objects in the scene 100% white and 100% selfillumination. you do not need lights for this pass. then, add black fog to your scene. adjust the thickness to your liking and render.

in combustion there's an operator called compound channel selection. apply this op to the footage to be blured and use your z-depth pass for secondary input. after the selection op, choose a blur op, after that a de-select op and your done. play around with the induvidual settings of each op, maybe though in some cc before you go into the compound channel selection.


Read my technical blog - lonerobot.net
  03 March 2005
I've had this problem myself - RPC objects will render out opacity in most render elements, but they blow up in Z-depth. I hadn't thought of it as being a Max issue, but it makes sense. The interesting thing is, how should z-depth rays react to opacity in textures? What happens when they hit partially opaque areas? I'd assume you should be able to set some threshold to avoid getting weird fringes on your trees and such.
My workaround was to render out a z-depth channel of just the terrain without the trees in the scene. That way, the trees get blurred at the same depth as the background. It seems to come out allright for the most part - the only potential problem could be if the camera passes too close to the horizon.
I'll try to decipher that Combustion message and use it next time.

The project:
  03 March 2005
pudgerboy - That is definately a creative solution to the problem. The only issue with that I can see is that RPC object have their own special maps. I don't think it will be able to recognize the opacity if the 100% white material is on it. I'll give it a shot though.

  03 March 2005
Here's an idea that just hit me - hide everything in your scene but your RPC figures. Render out a Z-depth pass as-is, and also render out a diffuse channel with alpha. In Combustion, add in the RPC diffuse layer. Apply blur with the new z-depth channel to just that layer and cut the whole thing out with the alpha channel.
If there are issues with the RPC objects showing tilted planes in your z-channel, try the "billboard" setting in the RPC object settings. That way (I think) your RPC objects will show up in your z-map as flat rectangles that float around and turh different shades of gray. Cut that out with the diffuse alpha channel and you've got a z-depth map that works for RPC.
I haven't tried this, so if it works let me know.
  03 March 2005
That sounds about right. Its a couple more passes, but those should be super quick passes.
The only issue I see there is when you have overlapping RPC objects. I'll try that right now.
  03 March 2005
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