Re: .mt vector question -again- clipped alpha in blur

[Rob Wuijster <rob(at)glassworksamsterdam.nl>]

Hi Matt,

Thanks for the detailed explanation, much appreciated.

vr.gr.,

Rob Wuijster

Glassworks Amsterdam
Keijzersgracht 473-479
1017 DL Amsterdam
T +31 (0)20-7940996
F +31 (0)20-7940997
E info(at)glassworksamsterdam.nl
W www.glassworksamsterdam.nl




Matt Lind wrote:
> I haven't used the built-in motion vector stuff, but when I was working
> on Barnyard I wrote a shader that outputs to .mt files for use with RSMB
> and had to deal with the same issues.
>
> In short, the motion channel is supposed to be jaggy because you want 1
> motion vector sampled per pixel.  If you anti-alias the motion channel,
> then you're effectively blending motion from multiple sources to come up
> with an average - which can be bad if multiple objects occupy the pixel
> and are travelling in different directions because the averaged result
> vector may not point in the direction either object is travelling.  This
> is why you may get weird artifacts in the blurring process.
>
> To get one sample per pixel, set min/max sampling to (0,0) in the mental
> ray options.  Also set adaptive sampling to a very high value (1,1,1,1).
> Same goes for motion sampling on the motion blur tab (1,1,1,1).  This
> will ensure one motion vector is sampled per pixel.  Using these
> settings should improve render times as well as your telling mental ray
> to do less work.
>
>
> Matt
>
>
>  
>
> > -----Original Message-----
> > From: owner-xsi(at)Softimage.COM 
> > [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Rob Wuijster
> > Sent: Wednesday, March 05, 2008 2:05 AM
> > To: XSI(at)Softimage.COM
> > Subject: Re: .mt vector question -again- clipped alpha in blur
> >
> > Hi all,
> >
> > Due to the lack of responses, I'm assuming nobody is using 
> > this "motion channel" output instead of the LaMaison shader? 
> > (rendering to 16bit RGBA SGI in both cases by the way.) I 
> > also noticed the "motion channel" 
> > render is all jagged.
> >
> > So, anybody used this new "motion channel" output with 
> > success and wants to elaborate on this? Tested it in Shake as 
> > well just to rule out any differences, this also doesn't work 
> > properly.
> >
> > cheers,
> >
> > Rob Wuijster
> >
> > Glassworks Amsterdam
> > Keijzersgracht 473-479
> > 1017 DL Amsterdam
> > T +31 (0)20-7940996
> > F +31 (0)20-7940997
> > E info(at)glassworksamsterdam.nl
> > W www.glassworksamsterdam.nl
> >
> >
> >
> >
> > Rob Wuijster wrote:
> > > Hi,
> > >
> > > I was looking for some old threads on the new .mt vector 
> > format, but I 
> > > cannot find the right info on this.
> > >
> > > If I add a channel for my pass, and comp the renders 
> > (beauty+mt) with 
> > > the RSMBVector plugin, the alpha on the blur is clipped, in 
> > comparison 
> > > to the LaMaison one.
> > >
> > > I can recall something about the .mt format and the inability of 
> > > adding an alpha channel, but cannot find the solution or 
> > more info to this so far.
> > > Testing in the FXTree, but this should probably the same for any 
> > > compositing app I guess...
> > >
> > > Anyone on this??
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