Vector Blur Problems

So I have this animation with shattering glass and a flying bullet and for some reason I I can’t get the motion blur or vector blur to render despite rendering it with the vector attribute and using (as far as I can tell) the right node arrangement. Any help?

I tried to upload the blend file but for some reason it’s not working.

The file’s probably too large – try uploading it to

Okay here is the file. Thanks for the tip!

I hope the URL works.

There’s a couple of adjustments you should make to your node setup:

  1. Your vector blur node is working OK, but it’s being “covered up” by the final Mix node at value 1.0, which takes the initial rendered image with the added Blur and Glare effects and composites it on top of the V-blurred image at full value. Drop the Factor value of this Mix node and the vector-blurred image will be revealed. You may want to reconsider using Mix, also, depending on your intent for combining the two effects pathways in that node. Or perhaps switch the input order so the vector blur is laid on top of the other effects.

  2. When you see what the Vector Blur node is doing with the values you have set you’ll probably flip out. The extreme vectors of the ejected particles cause it to render some outrageous streak effects, not really what you want, I’m sure. This is because you have set no pixel extent limits in the Vector Blur node – the Speed: Min & Max values. These limit the total extent of the blurring in terms of pixels. At min = 0 & max = 0 the max extent is basically unbounded, so the node tries to create what amounts to a nearly infinite blur length, with correspondingly weird results.

The minimum value sets a limit on blurring for small vector motions – a object has to move at least this many pixels in a frame for it to be blurred by the node. In the past (pre-2.5x), setting it above zero has caused artifacts I’m not sure have been addressed by the bug-stompers, so use it with caution. The max value limits how much blur is calculated for objects with very large motion between frames (in pixels). Set this from 20 to 50 or so to get a more realistic result from your shrapnel.

Hint: When building noodles (node setups) use Viewer nodes liberally at every stage of the processing to inspect the results, it makes it easier to troubleshoot issues like this, as you can see just where in the various node steps things start to go awry. It’s a good idea to remove them before rendering, though, since they do add to render time.

Thanks for the the tip! One last thing I’m trying to figure out it how to render out the 3d layer with alpha. Whenever I do the blurs are clipped by the alpha channel, so I loose any motion blur I was creating. Is there anyway to get alpha and blur in a render?

The only way I know is to send the alpha channel through a Vector Blur node that matches the settings of the one acting on the Image output from the Render Layer. The Alpha channel is an image also, so it can be manipulated in this way as well.

Another method is to take the final image composite and use it to make a greyscale mask that can be used as a sort of composite alpha. This can be tricky because some objects may have dark areas on them that will translate as transparency when made into alpha, when they should be opaque. So additional masking channels may need to be combined with the converted composite image to get a complete alpha mask. If you think of the alpha channels as 8-bit greyscale images, you can figure ways to use the nodes just as with the RGB image component, and add masks together, subtract them, multiply them, etc., to get the result needed.