How to map blur to position for film-jitter like effect

[paul_7484]

I am using the "wiggle" expression on Position to create a film jitter effect. 

How can I map a blur to the position of the layer, so that it blurs in relation to the movement caused by that jitter? I'm not looking to blur the images in the footage based on their 'motion' (ie - the baseball flies across the screen - I'm not looking to blue that) but just a motion blur based on the movement of the whole frame. 

[Mylenium]

Could be as trivial as feeding the wiggle() as a driver into a linear() expression to remap the value ranges. The only prerequisite would be for the wiggle() to exist on a "neutral" control before feeding it into anything or else you end up getting weird values and inconsistencies in the randomness. So apply the wiggle() to a custom expressions slider and then feed it into the position and blur with a pickwhip expression.

Mylenium

[Dan Ebberts · Accepted solution]

You could try applying a Directional Blur effect to your footage and tie the blur Direction parameter to your Position wiggle's velocity with an expression like this:

v = position.velocity;
-radiansToDegrees(Math.atan2(v[0],v[1]))

and use an expression like this for Blur Length:

m = .5;
position.speed*m

where you adjust the multiplier variable (m) to get the amount of blur you want. Something like that.

[paul_7484]

Thank you. I guess this is more invovled than I thought. 

Where do those expressions go exactly? The expression starting with v = goes in the Wiggle expression and the one with m = in the Directional blur? What is the syntax exactly? And then tie wiggle Position to Directional blur Direction with the pick wick?

[Dan Ebberts]

The first expression (v = ...) goes in the Directional Blur's Direction parameter and the second one goes in the Directional Blur's Blur Length parameter. No pick whipping necessary (assumes you already have a wiggle expression on the Position property).

[paul_7484]

Wow, holy hanna, that works great. Interesting effect. 

I've only used basic expressions before so I'll have to start some reading up to figure out how you did that. 

Many thanks for your help, that was really super helpful. 

[Dan Ebberts]

The key is that the Position's velocity attribute has the movement's direction information (you just need to use a little trig to convert it to degrees) and the Position's speed attribute has the movement's magnitude info.

[paul_7484]

Great, I will be reading up on how to use the expression syntax. 

[Dan Ebberts]

You'll find info on velocity, speed and radiansToDegrees() in the Expression Language Reference of AE's Help, and Math.atan2() in any JavaScript reference.