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Dr Dardis
07-29-2009, 01:44 PM
Hi All,

Does mental ray for Maya 2009 support sub-frame blurring with the rasterizer renderer? or am I doing something wrong?

I am getting linear interpolation of my blurs no matter what motion step I use. I have enabled "Export Motion Segmenting" in the export settings, which should enable true sub-frame interpolation if I have read the manual right.

Here are some images as an example. It is a bouncing ball at the top of its bounce, same object, same lambert shader, same frame.

It renders fine in 3delight (notice the arc to the blur)...
http://members.iinet.net.au/%7Ecdardis/Files/3delight.jpg

...but incorrectly in Mental Ray. What is worse, Mental rays blur is from frame 5.5 straight to 6.5! It has completely left out the ball's position at its actual key-framed apex (frame 6).
http://members.iinet.net.au/%7Ecdardis/Files/MentalRay.jpg

I can find very little about this on the interweb, aside from this cgtalk post from last year

http://forums.cgsociety.org/showthread.php?f=87&t=646949&highlight=motion+blur

... suggesting that it is a "current limitation" ;)

Does that limitation stand in the latest version? Any help or clarification would soothe my furrowed brow :cry:

Chris

edit* just did a check with the same setup up in Softimage, produces the same error there too... maybe it's a MR error across the board?

pap87
08-02-2009, 12:10 PM
In the quality section under motion blur in the render settings there is an attribute called "motion steps" that by default is set to 1. Setting this higher will sample the object's position more times creating that nice arc you got in the other render. Maybe something like 4 will give you a nice result.

Leffler
08-02-2009, 04:01 PM
In the quality section under motion blur in the render settings there is an attribute called "motion steps" that by default is set to 1. Setting this higher will sample the object's position more times creating that nice arc you got in the other render. Maybe something like 4 will give you a nice result.

Does this also add to the rendertime? I suppose it would, but will it be * 3 ?
Nice tip, thanks

Dr Dardis
08-04-2009, 04:27 AM
Thanks for the replies guys!

Pap87, thanks for that, but I already had the motion steps set to 7 and "export motion segments" enabled.

It turns out that MR for Maya does not "see" the transformation unless it occurs on a point-by-point basis (i.e. by deformer/skinning etc). the animation has to be on the shape node for segmented motion blur to work.

This is a bug. For more info, see my post (http://forum.mentalimages.com/showthread.php?t=5672) on the Mental Images forum.

The workaround in my case was to skin to a joint parented to the animated transform.

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08-04-2009, 04:27 AM
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