View Full Version : light trails

05 May 2010, 01:19 PM
Anyone have any idea what approach I would take to get this effect, as pictured in the photo below? Either in a 3D render, or in compositing app. I want to get curvy light trails from blurred highlights and light sources. Using motion blur in Mental Ray, I get bright streaky blurs off of highlights, but they are all straight lines, even when the object is moving erratically between frames. I guess Mental Ray calculates from one frame, straight to the next, regardless of what happens between frames. Whereas in photography the light will continue burning an image to the film as long as the shutter is open.

I have tried tweaking with the settings, and also various methods in After Effects.

Any ideas?

05 May 2010, 01:26 PM
have you increased your interpolation steps and maybe your frame range ? You should only be getting straight lines when using 1 interpolation step.

Depending on if your camera is moving you can do in post using motion trails ( well its called motion trails in combustions, im not sure about other compositing apps. )

05 May 2010, 03:16 PM
Thanks for the reply. :beer:

Well, like I said I get the blurs in Mental Ray, but that are all straight lines, seem to be calculated between positions at each full frame. I have tried cranking every setting I think. What settings do I need to make the blur conform to the sub fram motion, if possible?

Or, Doing it in post would be even better I suspect. I don't have Combustion, but I want to look into that. How does it work? Does Maya write vectors for sub frame animation, and then can motion blur in Combustion read that info to interpret the blur as detailed as the photo I posted?

05 May 2010, 03:20 PM
What settings do I need to make the blur conform to the sub fram motion, if possible?

Time samples and motion steps. BUt just to make sure you are rendering objects and not particles ?

Nothing complicated in combustion. You render out your animation with no MB and the combustion just blends frames in front or behind your current frame and overlays them on top of each other to give a blurred effect. Can work extremely well in some circumstances, much quicker and better quality than other more " real" effects in 3d.

05 May 2010, 03:42 AM
Ive done this before, I think its best to do in post, as irwit said combustion has a good effect.

To make the trails realy smooth - make a seperate pass of your glowing lights and render at a higher frame rate. Then apply trails and retime the layer down to the proper 25 fps or whatever you need.

05 May 2010, 04:29 AM
Cool thanks. Anybody try GenArts Sapphire, for After Effects?

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05 May 2010, 04:29 AM
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