Keyframing motion blur?

[robcat2075]

You can keyframe and vary certain camera properties like motion blur %

 

For demonstration this clip shows a ball that repeatedly moves in an arc over one frame. If there were no motion blur the ball would appear to stay in the lower left corner a it is always keyed there at the beginning of the frame.

 

As the motion blur % is increased from 0 to 100, the blur covers a greater portion of the path the ball travels during the frame.

 

This shows motion blur with 16, 25 and 49 passes and then the non-multipass motion blur.

 

BlurVarying_16_25_49_Post.mov

 

Multipass blur is more accurate if you use enough passes, but nonMultipass blur is way faster. In most situations (settings around 20% or less) the nonMultipass motion blur will work fine.

 

Notice also that nonMultipass blur is appropriately centered around the location of the object at the keyframed position, while Multipass blur actually stretches forward from the keyframed position.

 

This could be detrimental when an object needs to exactly be in contact with something on a certain frame, such as in a bouncing ball situation.

 

You could make Multipass blur be appropriately centered by offsetting your keyframes by a fraction of a frame. Tricky, but doable.

 

On the other hand nonMulti blur seems to have a limit to how far it can stretch; Multipass blur can stretch the full 100%, although there aren't many situations that you would want 100%

 

NonMultipass Blur can sometimes create weird results in complex motion situations, particularly on objects that are rotating more than they are moving linearly.

 

This clip shows 16 pass, 49 pass and nonMultiPass motion blur increasing from 0 to 100% on a spinning sphere that has been keyed to rotate 360° per frame.

 

BlurSpinning_16_49_Non.mov

 

But again, the nonMultipass blur will usually look fine at typical low % settings

 

 

PRJ: MotionBlurKeying.zip

 

 

 

Q: How is A:M's renderer more powerful than Pixar's?

A: A:M's renderer can accurately create arcs in motion blur

 

In interviews Brad Bird has expressed disappointment with the lack of arcs in their CG motion blur.

[John Bigboote]

Very enlightening, Rob. That illustrates the benefit of Multi-Pass rendering... Maybe Martin can sell Pixar some code...

[Rodney]

Interesting. You may want to add in a sequence to show how it looks without motion blur.

I know you explain it but... seeing is believing and would demonstrate the control.

 

For those interested in experimenting further, this is related to Xtas's MUFOOF effects and Vern's Subframe Rendering which can be used to great effect for spinning props, flame and lighting effects etc.

 

Facinating stuff.

[robcat2075]

Interesting. You may want to add in a sequence to show how it looks without motion blur.

 

With no motion blur both of the above examples would appear stationary and unchanging, since the ball is keyed exactly the same on each whole frame.

 

here is motion on an object that actually moves from frame to frame:

 

BlurInMotion_10_20_40_66_100.mov

 

The same 1 second motion repeated at 0%, 10%, 20%, 40%, 66% and 100% with 25 passes and again with non multipass blur at 0%, 10%, 20%, 40%, 66% and 100%.