Vray Vector pass in color for a compositing in Blender

I am compositing a scene rendered in Vray 3 that has a vector blur pass. The pass is in color and does not automatically work with the vecctor blur node. I have read that

Blender (Cycles) delivers a motion vector pass which contains

“R: pixel displacement in X from current frame to previous frame
G: pixel displacement in Y from current frame to previous frame
B: pixel displacement in X from current frame to next frame
A: pixel displacement in Y from current frame to next frame”
(Matt Ebb posted this on one of the threads)

I have used a seperate RGB to try to make this work but without success. Does anyone know what I should be doing?
Thank you

Don’t know if this works with Vray, but this does the job for Arnold and Mental Ray’s vector passes:

Most vector passes just include 1 transform in R/G channels. Blender’s vector blur node expects a second set in the B/A channels. If you don’t have it, you can just copy the R/G channels in and it will figure it out.

I have attached a split viewer that shows on the left side the vray vector export and on the right, the result using the channel separation. As the vray as blue in it, does the blue do anything?
Thanks for your reply


A quick google search would suggest no, the blue and alpha channels are just dummy data. Check them individually using the backdrop options in the node editor. If the blue channel is solid blue, or solid blue with black where there’s alpha, you can safely discard it and overwrite it with the red channel. If either blue or alpha seems shaded in a way that matches motion, there might be more going on.

Thank you for the response. The few blue parts are not covered by the alpha, but I am unaware of what the blue does.
On the other hand, the alpha can be used to help attentuate some premultiple issues.
Below is aen explanation for nuke that confirms what you wrote.

Many thanks helping with this.