disable camera MB

[Dubbie99]

Does anyone have any tricks for disabling camera motion blur for a particular object?
I am using the new spark SOP which has baked in camera MB.
I have tried a bunch of things but nothing has quite worked right.

I'm reluctant to render as a separate pass because there are a bunch of other objects in the scene that occlude the sparks, so I'd really need to use deep to composite properly.

[david.anastacio]

Hi,

You want all motion blur off , not only camera motion blur right? But I'm guessing as it is a deforming geo and you disabled velocity it has no geo (deform or transform) motion blur already, only camera.
Have you tried setting the geo sub steps of you sparks to 1 via the V-Ray object properties?

Best,
David.

[Dubbie99]

yes I tried that.

I also tried computing the inverse camera MB vector for each point, but I'm not sure I got my math right.

[Gosho.Genchev]

Hey Dubbie99 ,

At the moment we have no per-object control for camera motion blur specifically. I've tried doing exactly what you mentioned in your last post - bringing the camera in with an Object Merge, inverting the transform and generating velocity pointing in the opposite direction. It seems to work for me in my simple test case - could you please take a look and see if it helps for your scene as well?

Scene -> Link.

Best regards!

[Dubbie99]

Hi Gosho.Genchev
Thankyou for your example. I don't think your method can possibly work.

If you consider this picture:


The velocity of Point A and B is both {0,0,0} in world space.
The camera matrix difference is identical for both points A and B, and yet they each have a radically different velocity vector.

I think that it is essential to compute the vector in screen space.

My idea for an algorithm is this:

Get p_curr in screen space
Get p_next in screen space
vec = (p_curr - p_next) * 0.5
project vec to world space

I just need to actually get it to work haha

Thanks for your help anyway.

[Dubbie99]

After tying my brain into a pretzel, I finally solved this and it was simpler than I thought.