Question about vector blur

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Old 08 August 2012   #1
Question about vector blur

Is there a way to get a decent motion blur using vector blur if the character is not separated from the background?

I rendered out this image with velocity pass. When I apply vector blur using velocity as uv channels, they always look incorrect with weird hard edges. In this case, on the left side of the head.



Now if I use the character's matte as alpha, the motion blur turns out better and closer to what I expect. But overlaying it on top of the original non-blur image produce some very weird results.



Does this mean I should always render out the characters as separate pass from the background plate? Is there anyway I could make this work without separating them?
Attached Images
File Type: jpg vector-blur.jpg (20.9 KB, 38 views)
File Type: jpg vector-blur2.jpg (9.6 KB, 37 views)
 
Old 08 August 2012   #2
Try rendering out a single frame of rendered motion blur to compare it to. You might need to adjust the offset, scaling or direction of the vector blur and having a reference frame to compare it to might help get you closer to a higher-quality result.

Personally I'd forget about post motion blur and render the motion blur. Especially if your using a renderer like V-Ray to get physically-plausible lighting and shading it doesn't make sense to skimp on the quality by using physically-inaccurate motion blur. For the hit in render time you'll probably save yourself and your compositors a load of effort.
 
Old 08 August 2012   #3
Thanks Will! I haven't played with Vray motion blur yet, I should get to it!
 
Old 08 August 2012   #4
you really should render the fg and bg separate if you want to motion blur the fg.
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Old 08 August 2012   #5
you can add some blur to your vector pass in nuke...it will work for some case...
 
Old 08 August 2012   #6
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