View Full Version : Depth Buffer Question...

02 February 2003, 04:20 AM
Hey all, I have a scene of a hypervoxel explosion. It has a dust emitter and a dirt emitter. The dust is finished and I want to render it and get it out of the way so I can focus on the dirt, so I need to be able to composite them later. I have rendered a test of the dust with its alpha and depth buffer masks, and a test of the dirt with its alpha and depth buffer masks. I have applied the alphas to each of the images and have them on top of each other in two layers in Photoshop. Now I need to figure out a way to use the depth buffers to composite them properly. I have the two depth buffers, and I need a way to composite the two layers based on that. I'm having trouble figuring out how to do this. Any help would be appreciated.


02 February 2003, 03:42 AM
Yeah, I've been wondering this too! If anyone could shed some light (wave, haha) on this issue that would be great!!!! I know someone has to know how to do this.

02 February 2003, 03:45 AM
Would it be possible to show a sample image + alpha channel? I don't know the answer off the top of my head, but I know Photoshop well enough to take a stab at it and share what I come up with. :)

02 February 2003, 04:17 AM
k, here are the images I'm trying to use. Basically I have a pass of dust (that i'm satisfied with and it takes a long time to render, so i wanna render it just this once and be able to composite other stuff into it later) and a pass of dirt (still very much a wip)

I want the dirt to intermingle with the dust as if I had rendered them at the same time. I think you should be able to do this with the depth masks, but I'm not sure how.

Here's the pictures:

02 February 2003, 05:03 AM
Okay, I think I have it. I'm not quite sure though. Can you do a render of both at the same time so i can compare it against what I got? If it works, I'll share the technique.

02 February 2003, 05:10 AM
eh, I wasn't having too good results rendering them together, becuase it took so long to see the results of my your stuff, it's probably a lot better than what i've come up with in photoshop tryin to mix these layers

when I rendered them together it kept looking like they glowed...

02 February 2003, 05:40 AM
Hmm i don't think my idea works. I tried it with a cylinder intersecting a sphere and the result just didn't work.

I suspect that what I tried would result in a funky animation.


If I come up with something I'll let you know. Sorry :( I tried!

02 February 2003, 06:56 PM
Thanks for trying, NanoGator. I'm having a tiny bit of luck. I can get them to be on top of each other correctly, but it lowers their transparency values as well. I already have those set where I want them because of the alpha map. I need a way to select something, and then even if some of the pixels aren't 100% selected. To say that any pixels with a little bit of selection need to become 100% selected. That way it will leave their transparency values alone when I copy them onto a new layer, and won't make them more transparent...

Any one else have some ideas? This doesn't have to be done in Photoshop if that helps, but it seems like you should be able to.

Rumpus King
02 February 2003, 07:17 PM
Can't you just put the depth pass in screen mode on top of your color+alpha?

And do you have a specific reason for rendering seperate alphas?

02 February 2003, 08:59 PM
To composite a number of images with depth buffer information you are going to need either Digital Fusion or Adobe After Effects (Production Bundle).

PhotoShop doesn't understand how to use Z-buffer information.

Maybe there is a way you could comp the images together in Lightwave itself?

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