Problem with zdepth aliasing

[tricky]

I am applying DOF in post using an after effects plugin. The zdepth needs to be 'floating' as I may need to push it to exaggerate an effect, so I have unchecked 'clamp zdepth'. When I open up one of these zdepth renders, I am seeing harsh aliasing against the background. This messes up my DOF.



How do I stop this? I am using a Quadratic antialiasing filter at rendertime, but it doesn't seem to be affecting the zdepth.

[cheerioboy]

you want to turn off aliasing on the z-depth pass

here's a quote from somewhere on the internet

<quote>
If you anti-alias your Z-depth pass, any anti-aliased pixels would indicate wrong depth values and result in artefacts. In case of aliased Z-depth pass and anti-aliasing on the image, the passes don't align exactly which result in another type of edge artefacts. You can deal with the second problem by rendering your aliased Z-depth pass at double resolution. Add the oversized Z-depth pass and the image pass (scaled at 200%) in a pre-comp. Apply Lenscare and then scale the pre-comp back to 100% in another comp.
</quote>

[tricky]

I did wonder about this. I will give it a try. I assume a simple material overide (or the rendermask script) will enable me to render a double-sized zdepth quite quickly.

Request from Chaosgroup: can we have option to render out elements at double size?

To clarify, should I have 'clamp zdepth' ticked or unticked?
Also, in rendering the zdepth at double size, I should just uncheck any antialiasing filter, correct?
Should the zdepth pass be rendered with a fixed AA sampler, or should I still use my usual 1,4 min/max?

[tricky]

And another question - what's the quickest and easiest way to render out a zdepth pass? I was hoping to use the script 'RenderMask' but it doesn't seem to work for me (it just renders black)

[fewlo]

to just get the zdepth pass, how about turning off lights, ref/refract, maps and gi, then rendering the sequence, only saving the pass? Reckon that will be as quick as 'RenderMask'

[Morbid Angel]

Kind of why we render all utility passes as a separate job, double size, unfiltered etc. Tricky, if you see aliasing on the edges you can erode the alpha out a little bit to solve artifacts if you see any.

[squintnic]

you could render zdepth as an extratex with a falloff map set to distance as the texture.

[tricky]

Thanks all.