View Full Version : creating long motion blur trails

06 June 2007, 03:56 PM
Hey all,

I have a very large scene with many particles that are moving very fast. I want to create the effect of a camera with a slow shutter speed so that the particles have long trails following them. So I'm use mental ray motion blur and cranking up the settings but can't seem to get the right effect. I've tried increasing the blur by setting, bumping up the shutter close value to above 1, and changing the camera shutter angle to 360 and more degrees but I keep running into the same problem, the particles that fly by the camera really fast appear as a super grainy streak (not smooth). I've tried cranking up the time samples and the AA quality but it never helps (not to mention it increases render time a lot!).

So my question is: Is there another way to achieve this effect? in 3D or compositing?

Thanks in advance!

06 June 2007, 12:03 AM
A compositing app is where I would turn to try and do this. Using mental ray motion blur for this just seems like it'd take a long time to render. As for how to do it in a compositing app, I'm not too sure really. Maybe try to some motion trail filters or maybe you could get reelsmart motion blur to do it in some way.

06 June 2007, 02:07 PM
Thanks to the reply. I agree, compositing would be an ideal solution to the problem. I'm using After Effects to composite so if anyone has any ideas (compositing or other)... I also posted to the After Effects thread. Hopefully someone has some experience with this.

06 June 2007, 12:51 AM
I recently acheived this for a commercial project. We ended up baking our particle motion at a very high frame rate - something like 150 frames per sec or so - and then rendering out at that rate as well. That gave us plenty of sub frame samples to use time echo in afterfx with. Since we were moving very quickly and just wanted the particles to appear enlongated it worked out very well.

Good luck!

06 June 2007, 11:28 PM
Hey thanks for the replies. altruizine, thanks for the idea. Sounds like it should work well. I'm rendering out the scene now, but unfortunately it's gonna take a while (there are several hundred thousand particles in the scene!)

06 June 2007, 10:17 PM
i believe there is a plugin for AfterEffects by Trapcode called 'Particular' that is perfect for what ur trying 2 do.

otherwise, try using curve flow and try adjusting the opacityPP attribute and also using motion blur...

12 December 2007, 10:05 PM
Try the rasterizer in mental ray, it is very fast for rendering motion blur. Note that you have to increase motion steps to have the motion blur really follow the motion and not simply create a straight line.

CGTalk Moderation
12 December 2007, 10:05 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.