[Sidefx-houdini-list] deep primid aov?

eetu at undo.fi eetu at undo.fi
Thu Aug 14 04:56:39 EDT 2014

Hey Rangi,

That's where the beauty of deep data comes in! The aov values, as well 
as color and opacity, are stored _per_sample_, not per pixel, and that's 
why it works.

In nuke you can just select all samples that have a given id value 
(plus/minus a float epsilon..), and remove them or create a mask 

Matt: Apologies if the example scenes don't work at the moment, they 
were created with then-current versions of Houdini and Nuke (Dec 2013), 
and the deep handling has been changing a bit in both, I guess.


(apologies if this shows up twice, I didn't see my first try coming 
through, now trying with different from:address..)

On 2014-08-14 06:26, Rangi Sutton 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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