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Hopefully I'm asking this question correctly. Essentially I would like to animate a scene (baseball player hitting ball), add motion blur, and then animate a camera rotating around the player, but with only the ball blurred. In the final video composition, I want the motion blur applied to the ball to not be affected by the movement of the camera, but just the movement of the ball.

I want to capture this as if it were a still movement of an action scene, not something in motion. So I don't want the ball to actually move in the animation, just look blurred.

In real life I think you would stage a bunch of cameras around the scene and take a photo with all of them at the exact same moment, so when you string them together it looks like the camera is rotating around a single moment in time.

What would be the best way to pull off something like this?

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  • $\begingroup$ You want to recreate "Bullet time" effect from the Matrix movie. Normally in post you would use a vector blur derived from the motion of the animation, but you don't actually have any animation. I suggest distorting the ball object then change the material so that it goes transparent at the edges of its distortion. $\endgroup$ – 3pointedit May 1 '18 at 4:13
  • $\begingroup$ Yeah you nailed it, I was really trying to avoid using that term, ha. Thanks for the tip. Since a still render that includes the real motion blur is essentially perfect for one frame of this animation I'm imagining, is there any way to fake this in after effects? I'm curious if there's a way to string together a bunch of still images that I've rendered using motion blur and a baseball animation, but without actually animating the camera, if that makes sense $\endgroup$ – Chris May 1 '18 at 4:20
  • $\begingroup$ You would use a tracking application to determine the location of the ball over time, then generate a vector for it. Use this vector to blur the ball. But Blender can't do that. Unless you track the ball in the MCE then attach an empty to it. In 3D view attach a ball shaped plane to the empty and use its vector to blur the ball in the conpositor. You have to do this sort of thing with water simulations as well. $\endgroup$ – 3pointedit May 1 '18 at 4:35
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Bullet Time-without time

Fake bullet time effect

You can make a fake blur by distorting you key moving object. In this example I have used a lattice to bend the ball

lattice distort

Then modify your material with a graduated blend texture, to make the ball transparent at the end of its fake motion.

transparent material

Then your blur will cast the right shadow in 3D space, while a vector blur would not.

rendered blur


In order to 'fill in' the centre of the blurred ball you can add a Volumetric shader - similar to rendering smoke - using the same 'Factor' used to mix between the Diffuse and Transparent shaders to drive the Density.

added volumetrics

Maths nodes are used to manipulate the 'mix' factor to generate the Density and an RGB node can be used to ensure the same color us used for the Diffuse and the Volumetrics.

Increase the Render properties Light Path Volume bounces to 3 or 4 and this should produce the following results :

rendered

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    $\begingroup$ Nice solution. Could use some Volumetrics (Absorb and Scatter as for a very dense smoke) to fill in the centre of the mesh - so it doesn’t appear as a hollow shell. Currently you can see through the middle when viewed from the right angle. $\endgroup$ – Rich Sedman May 1 '18 at 9:23
  • $\begingroup$ Haha yeah I only noticed after I rendered it out, I shouldn't have tilted the track! But volumetrics is a good idea, I'm just not sure if you can apply textures/decals to it? $\endgroup$ – 3pointedit May 1 '18 at 12:31
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    $\begingroup$ I've added an edit to include the volumetrics to fill the gap - feel free to change or edit it as you like. $\endgroup$ – Rich Sedman May 1 '18 at 22:27
  • $\begingroup$ Looks good to me. Never occurred to me to edit other people's answers. $\endgroup$ – 3pointedit May 2 '18 at 2:06

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