FP Pflow distribution - Motion Blur issue

[Flyro]

Hello everyone,
I'm a student and we use Forest Pack Pro at school. I can't post in the Forest Pro section because the licenses are own by my school though..
I am making this post because we are facing a troubling issue with Forest Pack in Particle Flow distribution mode.
The motion blur generated by Forest Pack pflow distribution mode seems inaccurate. There is way too much motion blur on the mesh scattered for the movement made in the 3d scene by the particles (picture 1).

If the motion blur was correct, it should have been a very subtle blur in this 3d scene.

The only way I found to "fix" this issue is to disable the motion blur or to make the particles static. We can't reduce the motion blur on the Forest Pack by tweaking Vray Properties motion blur duration value, it doesn't affect the motion blur in the render.
This motion blur issue is present in every 3D scene I make, I think that the issue is related to the way the motion blur is calculated in particle flow distribution mode in Forest Pack.
You can try it by making a 3D scene with some particles moving, and scatter object on those paticles with FP Pflow distribution mode. Make another object which move at the same speed as your particles. Animate a camera that produces a certain amount of motion blur. You'll observe that your motion blur for your FP in your camera will be incorrect.

Is this problem well known and is there some solution to fix the motion blur?

Thank you so much for your help!

[Flyro]

Another screen to illustrate this issue.
The box in the red rectangle (it's not a FP, just an animated mesh) goes at the same speed as the boxes in the Forest Pack (pink boxes) in Pflow distribution.
You can clearly see that there is a motion blur issue for the forest pack.

P.S : This is only for the motion blur of the camera.

[Michal Karmazín]

Hi,

I've just done some tests with Forest Pack 8.2.6 & V-Ray 6 Update 2, but so far, I can't reproduce the reported problem. The motion blur amount applied to Forest items is identical to the "Shape Instances" within the PF Source (values in the VRayVelocity Render Element correspond between these objects). If you can reproduce it on a minimal scene, which you can send us, that would be great. Thanks in advance.

Best regards,

[Flyro]

Hello Michal,

I've just send the mail with the scene attached.
You'll just have to put yourself in the camera view, scroll through the frames (around frame 200 you will already see the problem), and hit render with the motion blur. Image attached for what you should obtain.

The green box goes at the same speed as the pink ones in the FP (the green ones go even faster than the pink).

I'm using Vray 6 update 1.2, Forest Pro 7.4.3, 3dsMax 2023 and Tyflow for the particles.

If you need anything else, don't hesitate. I hope i'm the one making a mistake.

Thank you so much for your help,

[Michal Karmazín]

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