Morning,

was following this thread for rendering velocity pass (Thanks!) -
http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=15521&highlight=motion+vectors [sidefx.com]

In the shot, i have a hammer swinging down in an arc - when composited in NUKE with vector_blur node, the blurring turn out more like a diagonal line instead of arcing. Tweaked “uv” and “offset” parameters and was never able to get the desired result as rendering motion-blur into the image.

Am I doing it incorrectly in NUKE, was my velocity pass rendered incorrectly or is it not possible to achieve similar result as rendered motion-blur using velocity blur since it's considered “fake” (image attached below).


Leading to two other questions…

1) What other reasons would one use velocity blur besides having the ability to control the amount of blur desired in comp & it renders faster motion-blur?

2) Why/What makes rendering motion-blur into an image slower?
Is velocity blur the ideal method used by everyone (especially in production), are there special cases where professionals would render motion-blur directly?

I must be searching the wrong places, cant seem to find threads/sites relating to them. Sorry to pack all my doubts in this thread and I understand this problem isn't entirely related to Houdini… But would deeply appreciate it if anybody can point me to them or give some insight!


eitht.

The nature of a 2d blur vectors is always linear. You'll never get curved motion - at least not with current techniques. The vector can only describe a direction and magnitude. If you want curved blur you'll have to render it.

The good news is mantra is decent fast at this. Play with the motion factor and xform time samples.

Ok got it, ended up rendering it.
Thank you for the tips, pinkwerks!

eitht.