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multipass
09-18-2008, 10:56 AM
Hi, im wondering if there is a way to control the look of motion blur with respect to where the solid mass is inside the blur.

if you make a sphere and run it across the screen, apply motion blur and render. the sphere is at the center of the blur. is there a way i can make the sphere at the front and all the blur behind it?

BeeVee
09-18-2008, 02:02 PM
Yes, change your shutter efficiency.

B

toby
09-20-2008, 03:34 PM
Interesting!
Efficiecny at 50% is a much more attractive blur, but doesn't blur as much.

Can you give us some background on this Ben?

Lightwolf
09-21-2008, 04:57 AM
Shutter efficiency controls how quickly the virtual shutter opens or closes.

If it opens/closes quickly, more "light" will be recorded at the beginning and end of the time slice that is sampled.
If it does so slowly, less will be recorded.

Effectively, a 100% efficiency will sample time in regular intervals during the Blur Length. This gives you a "smeary" kind of motion blur.
As you lower it, the samples will clump more and more around the central time of the sampling... the blur will fade out more and the ball (in this case) will be more prominently visible.

In a way, think of 100% efficiency as a straight line, 0% efficiency is more like a triangle.

@multipass: No, there is no way to shift the motion blur in time to achieve what you have in mind, that would require an extra control.

Graphically, that would mean skewing the tip of the triangle to the left or right (forward or backward in time).

63553
Red: 100% efficiency
Green: 0%
Blue/dashed: Hypothetical skew.

I hope it makes sense.

Cheers,
Mike