Anti-Aliasing on zdepth for combined geometry (and proxies)

[chris_koo]

We have houdini sims in which hundreds of objects are floating through space. For ease of use, we proxy these together so that we can then access the attributes more efficiently. However, there seems to be an issue where when setting the depth aov to be aliased, the areas where geometry overlap becomes anti-aliased. This issue occurs when combining the geometry as well and not proxy-ing them.

Keeping the geometry separate produces the desired aliased look

Attached is a simple render with two spheres, I A/B the graded depth in nuke to see the overlap areas. Bottom is separate, top is combined geometry

Also attached are our zdepth settings

[hermit.crab]

From what I tested, it seems that the overlapping areas are always anti-aliased regardless of combining geometry or not. Could you attach your scene?

EDIT: Turns out this is intentional and it is how the Z-Depth currently works.

[chris_koo]

Sorry, just getting back to this

Could there be a way where we can have the option to treat the zdepth much like the renderID aov works?

There is no anti-aliasing with the Render ID Render Element; where the edge of one object meets another object, the pixel color at that spot is the color from the object that contributes most to the pixel value

With the AA overlapping areas, we're getting false values with the interpolation. Which gets progressively worse with a scene that require massive dof

[hermit.crab]

Sorry, just getting back to this

Could there be a way where we can have the option to treat the zdepth much like the renderID aov works?

You could disable the Filtering of the element itself, however, this would disable the environment AA as well. You could render another one with filtering and combine it with the other one by masking only the environment edges

[chris_koo]

Filtering is disabled for the specific zDepth AOV and our hope is to achieve a zdepth pass with no filtering applied

Let me know if you need for me to upload a test Maya file. But, what we are finding is that when geometry is combined, the overlapping areas are getting filtered, despite filtering being off. When geometry isn't combined and overlapping, the edges are not filtered as expected

[hermit.crab]

Hm, you're right. I presume this is normal, but I'll ask the devs. Not sure if there are workarounds. For now, I suggest you try separating the objects.

[chris_koo]

The difficult part is that this occurs when you use vray proxies as well which is currently the only way to access attributes from Houdini with vray (as far as we know). So with our current workflow, it's either correct zdepth (which is important) or the ability to access much needed attributes, unfortunately we can't have both.

Would you be able to update me on what the devs say or even what the ETA could be for a discussion about this?

[hermit.crab]

FYI, I've notified the devs about the case. I'll answer back whenever I have more information.

EDIT: FYI, issue is logged (internal bug-tracker id: VMAX-13586).

[hermit.crab]

Hello again. After the dev analysis, it turns out we have already thought about this. The "Deep merge fragment mode" within the VRayOptionsRE is an option meant to combat this. If you set it to either "By Z-depth" or "By Render ID and Z-depth", there shouldn't be any AA in combined geometry.

EDIT: VRayOptionsRE is not available in Maya, will write back after I see if there's an equivalent.

EDIT2: It is located in Render Settings > bottom of Render Elements tab > Deep merge mode.