Hi guys, ive got a bit of problem with generating velocity blur for my particle system. Im not sure what is the correct method of creating particle velocity blur that takes into account camera blur as well. Im using houdini 8 for this. Its been giving me a real head ache.

Does anyone have any tips for doing this? Or a digital asset/hip file?

Anyhelp at all would be a great.
Thanks in advance
Nick

Do your particles have a velocity attribute? They should. Then in mantra ROP select “Velocity based motion blur” - or something similar. I'm on 9 now…

This stays valid unless you're rendering sprites. If so you need to send to mantra velocity attribute separately. Look into Render Tab of your object for something like Procedural geometry (Render as -> procedural), then choose proper attributes from pop up window.


hope this help,
sy.

from what I remember the Eight has ‘velocity mb’ and ‘deformation mb’, those are in Mantra op, for particles use velocity mb,

put down ROP network, go inside and put there Mantra op, don't forget also add Cache op in SOP to have MB correct calculated,

The problem is not in getting velocity mb blur to work at all, its the fact that the results are incorrect.

Imagine a fast moving camera that is tracking the dust coming of the wheel of a fast moving car, at render time mantra doesnt know how to combine particle velocity with the cameras velocity properly, so you end up with heavily smeared particles where there should be little if any blur… for example, even if the dust is moving forward along with the car and camera at the same speed (i.e. would appear to be static from the pov of the camera during the animation) you end with heavy motion blur where there shoudnt be any.

It appears velocity blur only works correctly with a static camera.
If you know how to manipulate the velocity attribute to conpensate for the cameras motion that information would be much apreciated

Cheers
Sergio

Import the camera into SOP level of a new object. Do the same with your particles/geometry. Compute particles velocity relative to camera.

Got some old example with SOPs. This can be done in flexible way in VOPs also.

hope this help,
sy.

Thanks Symek!

Think I understand how/why that works, we'll try this out on the actual shots.

Still it's mantra that should be doing this, not us.

cheers
Sergio

I would prefer to have a choice of tweaking anything I want!
But I get your point.


cheers,
sy.

I like the power to mess around with it too

But this is a weird/annoying case because we are using it to achieve what should be default behaviour.
It should be the other way around… in those rare cases when we want velocity blur to do something out of the ordinary then by all means force us to mess around with velocity attributes!

S

Nice one SYmek Exactly what we couldnt figure out. Ands it a pretty simple solution compared to the ones ive been trying. Cheers
Oh aye thanks to Serg for following up on this!

Thanks
Nick

Hey there,

I've been trying to figure out how to render proper trails // curved motion blur s for my particle system. Since, rendering based on velocity blur is not the answer, I tried to cheat by creating some trail particles and creating a trail geometry.. However, It wasn't what I was looking for.

SYmek's technique is just what I was looking for actually, However, I managed to render the proper trails just once or twce, then it stopped rendering. I was wondering If any of you guys managed to get proper trails / mblur out of particles.

If yes is it possible to post a simple hip file or give some tips.

cheers…

cellchuk
Hey there,

I've been trying to figure out how to render proper trails // curved motion blur s for my particle system. Since, rendering based on velocity blur is not the answer, I tried to cheat by creating some trail particles and creating a trail geometry.. However, It wasn't what I was looking for.

SYmek's technique is just what I was looking for actually, However, I managed to render the proper trails just once or twce, then it stopped rendering. I was wondering If any of you guys managed to get proper trails / mblur out of particles.

If yes is it possible to post a simple hip file or give some tips.

cheers…

All should be fine now:

I changed object for H9 one for proper Geometry Velocity Blur paramter.
I choose a right sop for rendering (the last one has velocity attr = 0).
I made a new Mantra ROP.
It seams to work now.


cheers,
sy.


BTW: As far as I remember this file is not mine. I've found it somewhere I think. Don't remember, sorry.

hey Simon,

thanks for the quick reply. and the sample file. that helped a lot.


cheers,
selcuk