how could you get light streaks in motion blur

[Pete]

Hi there,
Just wondering if anyone knows how to get an effect like this where the highlights and light sources leave a solid streak?
The motion blur is a bit scarey in MR and I havent touched it much but as far as I know it would just smudge any highlights out...
Pete

http://www.peterleary.net/forumfiles/pebbles-montage.jpg

[farhaad_yousefi]

if there is a good and full solution for this beauty ..count me in class too.!! ;)

[scaron]

one ways of doing something like this is to use particles, MT MG 2.0 plugin has a cool mesh trails feature.

unfortunately motion blur would be the only way to get the camera motion to be included. essentially you need a way of accumulating the position of the light over time and motion blur is the only way to do temporal sampling

maybe some guys that are good with a compositor can share their post techniques? maybe a custom matte pass that used a simple sphere with no shading just constant white, load the sequence in with as many offsets as you need, add* them over each other, and multiply that down on top of a color?

*i meant add (A+B)

[cryptosporidium]

i think this is a typical work for 2D. even if it would be possible to render (i mean truly render, not just fake it by particles or something), it would take disgustingly long time.

regarding 2D way how to do that, it depends on software you use, but roughly i would try following:
1)track the points you need to leave streak
2)connect either particle emitter or paint tool
3)adjust the look of the particles/paint, add some glow and stuff
4)render
5)show to friends
6)share it here .-)

[skyphyr]

There are two key factors to getting that type of effect with motionblur.

I'd suggest using the rasterizer and you'll need a fair number of motion samples to get the curve smooth and following the detail of the movement.

The other is to be using values that go well over 1. Imagine where 1 would get it white for the exposure time of a frame then to get it blowing out to that kind of level with motion blur you'd need it to be X times brighter where X is the inverse of the frame exposure fraction the object spends in front of any give point. So say it spend 1/10th of a frame's exposure over a pixel - you'd need it to be a value of 10 to bloom like that.

Cheers,

Alan.

[Pete]

The other is to be using values that go well over 1. Imagine where 1 would get it white for the exposure time of a frame then to get it blowing out to that kind of level with motion blur you'd need it to be X times brighter where X is the inverse of the frame exposure fraction the object spends in front of any give point. So say it spend 1/10th of a frame's exposure over a pixel - you'd need it to be a value of 10 to bloom like that.

What values would you adjust over one? Wouldn't they just get smudged out with the motion blur anyway?

(Thanks for all the replys by the way)

[skyphyr]

Hi Pete,

The reason things seem to get smudged out is because they're only over that point for a fraction of the exposure. Say there a 5 evaluations and the background is black but for one of those evaluations something white goes over it. You'd average all the samples so you'd get ( 0 + 0 + 0 + 0 + 1 ) / 5. Which is 0.2 - quite a dark grey. But if in that case you'd used 4.5 for the brightness of the object you'd get 0.9 instead. So it wouldn't seem so smudged out.

Cheers,

Alan.