Motion Blur … present but not blured

[Oleg Pirogov]

>But … do we know precisely what AE needs to compute a motion blur ?
>The position at every frame is clearly insufficient …
>The position at every thisComp.frameDuration/10 ? … thisComp.frameDuration/100 ??
Well, preferably, position at every point on the timeline. But since you have 16 Samples per Frame in the settings, ~16 discreet values per frame would arguably be enough.

On the other hand, your speed is polynomial function of time:
-SpeedCoef*(tt-t0)*(tt-t1)
– why not just compute (I mean, with pen and paper) its primitive integral and use it instead of numerically integrating speed 16 times per frame?

[Steve Bentley]

I am wondering if the issue is one of “remembrance”. There is no memory of the frame before when using expressions. The motion blur algorithm needs a delta between the frame before and the frame to come, neither of which are being calculated on the current frame. I use expressions all the time and get motion blur correctly so I’m not sure what the difference is here. Did the project get uploaded so we could play/

[Oleg Pirogov]

>The motion blur algorithm needs a delta between the frame before and the frame to come, neither of which are being calculated on the current frame.
As far as I understand it, motion blur just renders the layer at [Samples Per Frame (or more, up to Adaptive Sample Limit)] points in time taken uniformly(?) from the scope, defined by Shutter Angle and Phase.

[Steve Bentley]

Right but it would have to have a vector to figure out which way the blur should go. And while expressions will still provide that, this one doesn’t seem to or is giving an error.

[Steve Bentley]

I think i’m a couple of posts behind. Once I posted there were a bunch in front of mine that weren’t there before.
Did the OP ever post the project?

[Oleg Pirogov]

>Right but it would have to have a vector to figure out which way the blur should go

I don’t quite see why it needs the vector. In my understanding, Motion Blur just overlaps a number of rendered images of the layer mimicing real-life camera behavior rather than interpolates between frames.

>Did the OP ever post the project?

No not yet. Though you might be interested in recreating something similar by simply applying 10*timeToFrames(time); to, for instance, an X Position of some layer and turning on motion blur. I’m convinced it results in the same thing as in the OP’s project.

[Nicolas Guionnet]

Yes, Oleg, of course …
This is what I did … finally. ????

But, in the future, I would have been tempted to use more sophisticated functions (like a Gaussian) … that require fare more than a pen to provide their primitive … if this numerical computation had been efficient …

Thus, I will use simple functions …

[Nicolas Guionnet]

>Did the OP ever post the project?

I don’t know what an OP is … but I suspect that it could the guy who started the topic, alias me.

Sure, I can upload the file but as it uses a load of imported .ai files … I don’t know how to do that … properly.

> In my understanding, Motion Blur just overlaps a number of rendered images of the layer mimicing real-life camera behavior rather than interpolates between frames.

As I said, I tried to change the computation step to thisComp.frameDuration/10, this way providing 10 times more vector images. And indeed AE used them to make a better motion blur. The “sample per frame” option (composition settings > advanced ) determines the number of images that will be used for the motion blur. If you reduce it to 1 or 2 , you get the same poor motion blur issue we were talking about. So I guess AE “tries” a sequence of time values, close from the current time, to compute the needed images through the expression, and then superposes them. If there is only one image per frame provided, it superposes the image on itself …

[Steve Bentley]

You can just drag the project into the message box (where you type) and the COW will look after the upload for you.

[Nicolas Guionnet]

Let’s try :

13237_machinebug.aep.zip