(Fixed) [HOU-2535] velocity + camera blur broken (even more urgent)

[LeoYfver]

vray dont evaluate motionblur with velocity correct.

for example the velocty is in the x axis and both camera and velocity object are moving up synchronized.

centos 7
houdini 18.0.499

V-Ray for Houdini number:12071 hash:6fe7ab3 from 15 Apr 2021 02:02 (build number:12071)
V-Ray Core 5.00.50 [fcc821e3] from 31 Mar 2021


mantra

vray:

viewport:

[LeoYfver]

this is fixed in latest nightly, thanks!

[LeoYfver]

This was more complicated then i thought. The behaviour match mantra 100% percent now but its not what i expect. Its different when animating the geo node vs animated the geo inside with a transform node.

frame 1001:



frame 1002 (1 unit up):



rendered frame 1001:

what i expected( when having the animated transform on the geo node):



what i got(when having the transform inside the node):

[Gosho.Genchev]

Hey Alexis,

As you've mentioned, there's a reason for this happening:

1. The camera is moving up so any geo in the frustrum will be blurred in that direction.
2. With the "transform" node, you have the blur from the "v" attribute pointing towards the camera. So the blur will go towards the camera, and then face downwards.
The downward blur effect is counteracted by the object-level animation that matches the camera animation -> therefore, no up-down blur going on.
3. With the "geo_transform" node, you don't have the upward movement to counteract the camera movement. You've added a Transform SOP at the bottom but it is not affecting the velocity attribute - with the setup in "geo_transform", the "v" attribute is the only thing affecting the motion blur, and the final "transform2" node does not affect the "v".

A couple of suggestions:
1. Maybe you could bring in the camera and calculate its velocity with a Trail SOP (change it to Forward Difference, instead of Backward), then add it to the "v" attribute of the particles.
2. You could disable "Camera Motion Blur" in the ROP settings.

Example for (1):



If there's anything we can do to help out (I suppose your setup is quite complicated and this scene here doesn't really respresent the issue you're facing), please do ping me.

Best regards!

[LeoYfver]

Gosho.Genchev thanks for the explanation. The solution we use right now is basically counterbalancing the velocity

Im just imagening if i have spheres that are moving towards the camera in a real life situation and both moved together in sync we would have the sphere mobluring like both where standing still.

Thanks for the explanation and now i have a more clear visual of whats going on

Regards Alexis

[Gosho.Genchev]

Im just imagening if i have spheres that are moving towards the camera in a real life situation and both moved together in sync we would have the sphere mobluring like both where standing still.

Yes, of course. The thing is - in the second example the renderer is not supplied with the information that the spheres are moving up. The motion blur algorithm is only told that they're going forward so it's blurring them in that direction based on the velocity. Then it's also blurring them downwards based on the camera movement :shrug: The missing part is the blur going upwards (because they are indeed also going up) but that info is missing in case (2).

Good to know you've found a solution.

Best regards!

[LeoYfver]

Gosho.Genchev thanks for explaining gosho!