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Light Trails

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Gully Moore
Light Trails
on Feb 13, 2009 at 7:45:13 pm

Is there any way to make after effects pick up bright light and then as the camera moves it creates a motion blur or some kind of extention of the light?

So if for example someone was holding a torch in the air, how could i make a trail of light as they pull the torch down?

Thanks


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Kevin Camp
Re: Light Trails
on Feb 13, 2009 at 9:00:42 pm

if you are creating light streaks from footage, cc time blend or echo would help to create this effect. they both will take frames previous frames and composite them on the current frame to generate a motion blur like effect (like light streaks).

with cc time blend, set the 'clear to' to current frame, adjust accumulation to suit (higher values add more frames, lower fewer) and try a few different transfer settings (blend is the most natural, but screen or add may work better for bringing out the light streaks). also, time blend is kind of tweaky, so after any change you make, hit the clear option in the effect.

echo is less tweaky, but a bit slower... set the echo time to 1 divided by your footage's frame rate. adjust the number of echoes and decay rate as needed. set the echo operator (blend mode) to get the desired effect.

you could also try timewarp... it will try to generate motion blur thru interpolation calculated from pixel motion (tracking pixels as the move from frame to frame). set the speed to 100, then go to the motion blur settings to try and increase the motion blur. it's unlikely that it will produce long light streaks, but it may help to smooth the motion out to further effect with cc time blend or echo or some other method.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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Viacheslav Sasykin
Re: Light Trails
on Feb 13, 2009 at 9:49:28 pm

I would say there are 3 ways you can achieve it.
The first is honest way - as Kevin suggests through the Time filters in AE.
The second one is a trick, to see what I mean, watch this tutorial:
http://www.videocopilot.net/tutorials/3d_sparks_title/
may be it`s not exactly what youre after but you`ll get an understanding of moving objects in 32 bit color space with blur applied and how it looks like.
And the third one is a pure simulation, tutorial is here:
http://www.videocopilot.net/tutorials/light_streaks/
Hope you will find something that you need.



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Jon Geddes
Re: Light Trails
on Feb 13, 2009 at 11:26:10 pm

I think the effect he is looking for is described in this tutorial...

http://www.videocopilot.net/tutorials/earthquake_with_32bpc/

(yet another video copilot tutorial)

It explains how to convert 8-bit footage into 32-bit which causes the lights to streak naturally with motion. Then again I could be wrong and he could be looking into how to create those huge timelapse streaks of light which would be in the other tutorial mentioned.

Jon Geddes
Motion Graphics Designer
http://www.precomposed.com


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Gully Moore
Re: Light Trails
on Feb 15, 2009 at 4:04:56 pm

ok thanks guys, i'll have a play around - already liking the cc time blend if i add a mask so it only affects certain areas :)






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