Heya everyone,

Got a bit of a puzzler on my hands. I've got a matchmoved sequence with fairly severe motion blur. The matchmove itself is decent, and in the viewport it seems the my geometry is tracking the features perfectly (well…you know, ALMOST perfectly).

Sadly, when I render with Motion Blur (deformation) at a positive shutter speed, the motion blur seems to lead the plate, while a negative shutter speed makes it lag.

I've attempted to offset of matchmove data by fractions of the shutter speed (thinking foolishly that perhaps I can offset the camera, by half the shutter speed, I might be able to get closer), but instead found that it looks like a strange hybrid of both… and decidedly NOT better.

If anyone has any thoughts on the matter, i'd love some insight.

Cheers,

G

Hey Gene,
Can you do Velocity blur? It's a lot easier to control which way the blur goes in that case. You can put down a Cache SOP, set to range $F $F+1 and use an index of $F+1. Then use a Point SOP to calc the velocity ($TX - $TX2). I believe you can then offset the index as well, using $FF + .5 or something like that, making sure Blend is turned on in the Cache SOP. Or something along these lines, I can't test it right now. Then you can mult the velocity or offset etc, to get “forward” motion blur. In 8.1, by default you can really easily only get frame-back blur which often doesn't match the plate.
I've heard rumours a future version of Houdini may address this in a good way

Cheers,

peter B

If you want frame centered motion blur can't you just render on non integer frames?

Say your shutter is .4 then in your frame range you would render frames 0.8 to 299.8 at 1 frame increments.

One thing to note though is that shaders are evaluated at shutter open ( $F.8 ) so you'll need to be aware of that.

Thanks for the feedback gentlemen,

your insight are much appreciated – will try later on today, and post an update.

Cheers,

G