[Sidefx-houdini-list] unpremultiplied rendering?

Larry Giunta larry at gcreativestudios.com
Mon Jul 19 11:27:12 EDT 2010


We just delivered a bunch of unpremultiplied elements for a project  
and running it through the premult COP, as Martin suggested, worked  
just fine.

As for the goal. The main reason we get requests for un-premultiplied  
passes is usually when it's a keyable element ( intended to go over  
footage or a live feed, etc),
and the rendered element has transparency of soft/ramped edges ...or  
motion blur etc.
If you try to use a premultiplied pass you tend to get black edges or  
halos. But if you use a straight pass you'll usually get the clean  
look you expect.

Larry




On Jul 19, 2010, at 11:07 AM, katrin schmid wrote:

> hi,
> there are renderers that make it an option
> mental ray for example.
> No political intentions, just a user request
> and i didnt really follow up what the goal is.
> Regards,
> katrin
>
>
> -------- Original-Nachricht --------
>> Datum: Mon, 19 Jul 2010 10:58:47 -0400
>> Von: John Coldrick <jc at axyzfx.com>
>> An: sidefx-houdini-list at sidefx.com
>> Betreff: Re: [Sidefx-houdini-list] unpremultiplied  rendering?
>
>> On Monday 19 July 2010 01:53:46 am katrin schmid wrote:
>>> hi,
>>> i have been asked to unpremultiply passes post render.
>>> Which sort of lets me wonder if we i couldnt render this way in  
>>> first
>>>  place. Anybody know how to do this?
>>> Best Regards,
>>> katrin
>>
>> 	Yeah, AFAIK there's no way to render this out directly.  You  
>> might want
>> to
>> mention that every 3D software package in the world renders layers  
>> this
>> way,
>> and many compositing packages like Nuke even have a handy button  
>> on the
>> read
>> node to deal with this invisibly...
>>
>> 	Never mind, that will just cause trouble.  I hate political stuff  
>> like
>> this
>> instigated by people that don't understand the tech...
>>
>> 	*sigh*
>>
>> 	Cheers,
>>
>> 	J.C.
>>
>>
>> ---
>> John Coldrick
>> 416-504-0425
>> jc at axyzfx.com
>> --------------------------------------------------------------------- 
>> --
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>>   - Quentin Crisp
>>
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