Deep Raster Problem

[djpeanut]

Hi, again (!)

I've got a piece of geometry shaded with a VEX Super Material shader, and it's representing a water surface so it's pretty reflective. I'm also trying to render in a depth plane using Deep Raster in Mantra so I can generate some background fog in COPs. But the reflective surface gives me lots of depth plane artifacts, meaning that I get lots of little white patches when I apply the Fog COP.

Anyone have any ideas for how to stop this? I just want the water geo to return it's own depth, not that of stuff reflected in it.

[edward]

Maybe you can render the water in a separate pass without reflections. You can then do a Zdepth composite.

[sibarrick]

Are you sure they aren't holes? do you have displacement on your water. Try turning up displacement bounds if you do. Displacements are the root of all evil if you don't know what they are doing in the renderer. Good thing to read up on.

[malexander]

If you do end up with a few holes, you could use a Median filter (Median Cop) to remove the specks. But your image shows large bands of 'bad' depths, so you'd still be stuck with those.

If all else fails, try rendering out your scene as a Z map only, minus reflections and anything fancy, and see if the artifacts are still there.

[djpeanut]

Are you sure they aren't holes? do you have displacement on your water. Try turning up displacement bounds if you do. Displacements are the root of all evil if you don't know what they are doing in the renderer. Good thing to read up on.

17447[/snapback]

No, there's no displacement happening, it's just a grid with a Point SOP with some expressions rendered as subd. I'll try and figure out that Z-depth compositing stuff you people keep mentioning

Thanks!

[djpeanut]

If all else fails, try rendering out your scene as a Z map only, minus reflections and anything fancy, and see if the artifacts are still there.

17460[/snapback]

Erm... how do I render out a Z map only?

[Jason]

Erm... how do I render out a Z map only?

17572[/snapback]

Hey djpeanut,

You can ask mantra to render it by putting a -Z on the commandline in the Mantra ROP. One thing to be aware of, though, is that mantra will antialias the edges of your objects and thus you end up with z values which don't make any sense on the edges. This is because it antialiases to black, which in a z image is right on the camera. To get around this, you may find that you'll have to unpremultiply the Z depth map in COPs (or whereever you're comping).

ZDepth compositing usually leads to all kinds of badness due to things like these. Motion-blur and internal edges (not the silhouette edge) will suffer from antialiasing too. Having one pixel, filtered or unfiltered, is not enough information to reconstruct built-in z-depth effects in many cases.

Post your results:)

[djpeanut]

Thanks Jason, I'll post some results when I try it out tomorrow.