[Sidefx-houdini-list] deep primid aov?

Matt Estela matt.estela at gmail.com
Thu Aug 14 00:07:50 EDT 2014

Interesting. I had someone on odforce send me their solution which I'm
studying now, their attached screenshots look like its handling motionblur
and antialiasing correctly:


Having problems making it work locally though; the exr's made when I output
deep aov's appear broken in rv and nuke (like the channels are being
shifted by one and affecting the main rgb layer), and nuke itself is VERY
crashy when you abuse deep files. Gonna keep playing with it, will let you
know how I go.

Cheers for the feedback, I won't feel so bad now if I can't get it to work.


On 14 August 2014 13:26, Rangi Sutton <rsutton at cuttingedge.com.au> wrote:

> Hey Matt,
> I don't think it can be tackled like you're describing.
> If you say the value identifying the object is  "5", how does the deep map
> say it's 40% of 5 if it's not saying it's "2"? It needs two bits of info,
> the fact it's "5", and the fact it's "40%".
> You'll need a separate channel for each component you want to be able to
> separate, so you're back to multiple AOVs.
> Or you embrace that you're working in deep land and render a separate pass
> for every object and deep merge the lot.
> ID passes where values rather than channels are used to seperate the
> objects is a hack that falls over wherever any sorts of transparancy,
> including anti-aliasinng or motion bur, comes in to play. Making it deep
> just amplifies the problem.
> Cheers,
> r.
> Rangi Sutton
> VFX Supervisor
> Cutting Edge
> On 13 August 2014 12:38, Matt Estela <matt.estela at gmail.com> wrote:
>> Short version:
>> Outputting primid as a deep aov appears to be filtered to nonsensical
>> values, is that expected?
>> Long version:
>> Say we had a complex spindly object like this motorcycle sculpture created
>> from wires:
>> http://cdnl.complex.com/mp/620/400/80/0/bb/1/ffffff/dad2da95038d2c19ee6f7207eacf5e0c/images_/assets/CHANNEL_IMAGES/RIDES/2012/04/wiresculpturerides01.jpg
>> Comp would like to have control over grading each sub-object of this bike,
>> but outputting each part (wheel, engine, seat etc) as a separate pass is
>> too much work, even outputting rgb mattes would mean at least 7 or 8
>> aov's.
>> Add to that the problems of the wires being thinner than a pixel, so
>> standard rgb mattes get filtered away by opacity, not ideal.
>> Each part is a single curve, so in theory we'd output the primitive id as
>> a
>> deep aov. Hmmm....
>> Tested this; created a few poly grids, created a shader that passes
>> getprimid -> parameter, write that out as an aov, and enable deep camera
>> map output as an exr.
>> In nuke, I can get the deep aov, and use a deepsample node to query the
>> values. To my surprise the primid isn't clean; in its default state
>> there's
>> multiple samples, the topmost sample is correct (eg, 5),  the values
>> behind
>> are nonsense fractions (3.2, 1.2, 0.7, 0.1 etc).
>> If I change the main sample filter on the rop to 'closest surface', I get
>> a
>> single sample per pixel which makes more sense, and sampling in the middle
>> of the grids I get correct values. But if I look at anti-aliased edges,
>> the
>> values are still fractional.
>> What am I missing? My naive understanding of deep is it stores the samples
>> prior to filtering; as such the deepsample picker values returned should
>> be
>> correct primid's without being filtered down by opacity or antialising.
>> Stranger still, if I use a deepToPoints, the pointcloud looks correct, but
>> I'm not sure I trust the way it visualises the samples.
>> Anyone tried this? I read an article recently were weta were talking about
>> using deep id's to isolate bits of chimps, seems like a useful thing that
>> we should be able to do in mantra.
>> -matt
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