vector passes

[cdavis]

Im rendering a camera move over a load of 3d rubys ( lots of reflection & refraction) but the compositor is saying the vector passes dont look right & they should be on black not on mid grey.

Is there any specific workflow to rendering these vectors out & using them in nuke?

[joconnell]

Here's the workflow I use in nuke / vray max.

Add a vray velocity element and turn off clamp colours, change nothing else.
In nuke add a vectorblur node directly to your render. Leave the channels it affects to all, for your uv channels use the vray velocity pass. Set your method for blur to forward, and choose the regular rgb.alpha as your alpha channel.

With this the motion blur amount becomes the same as your blur duration. 1.0 is one frame of blur or a 360 degree shutter angle, 0.5 is a half frame of blur or a 180 degree shutter.

Mid grey is kind of a throw back to clamped colours where you only have values between black and white. mid grey essentially becomes no blur, values over mid grey are blurs in one direction and values under grey are blurs in the opposite direction. With proper floating point values, you can even get negative colours and it'll still work perfectly.

[Yannick]

Hi Chris,

for the velocity pass in Nuke, you usually have to swap the red and green channels.

Yannick