Velocity channel problem

[tricky]

I'm using a post-production plugin called 'ReelSmart Motion Blur Pro Vectors' to add motion blur to an animation in after effects. This is one of the frames of VRayVelocity.



I've been getting weird results, so I emailed the company who make the plugin and this is the response:-

"The MotionVectors you provided are not in a form we support:
1) You can use the Mental Ray support in Max and do a second pass, instructions here:
http://revisionfx.com/support/faqs/motion_vector_FAQs/motion_vectors/#3d Max 8 And Up
2) I am not quite sure what is going on with the VRay shader, it looks like it is clamping the raw floating point value to 1.0 instead of scaling it to fit the 16b image (with what we call Max Displace) -- perhaps leaving you with only motion of 1.0 or 0.0 pixels in that case.
Of course since you have AE 6.5 you cannot try in floating point"

As far as I can tell, I have left the default settings for the channel:
clamp velocity= ticked
max velocity= 1.0
ignore z direction = ticked

[instinct]

The velocity is saved as "Pixels per Frame" with these settings. Do a testrender in the frame that has the most movement and take a look at the last frame max velocity. Set your max velocity above that value
and things are scaled rather than clamped.

[tricky]

The velocity is saved as "Pixels per Frame" with these settings. Do a testrender in the frame that has the most movement and take a look at the last frame max velocity. Set your max velocity above that value
and things are scaled rather than clamped.

Instinct: could you ellaborate? I don't quite understand what you are saying. The camera movement is reasonably constant and slow: about walking pace I'd say.

[instinct]

Well, but it is probably still above 1. So that gets clamped. Setting the max velocity means that this value will end up as beeing 1. So for example when set to 10.0 then a velocity of 10 will end up as pixelvalue 1, a velocity of 5 as 0.5 etc. This way you can scale the velocity within the 0-1 range. The lastframe spinner (the disabled one) is telling you the maximum velocity of the last rendered frame, wich you can use to find out what your maximum velocity (in pixel/frame!) was and set the max velocity accordingly.

Regards,
Thorsten

[tricky]

Clearly I'm going to have to play around with this. I haven't used the velocity channel for a long time - in fact, when I did use it in the past, it was before the VrayVelocity element was available, so I just used the built in one and saved to RPF files. I don't recall having to change any values then: just save the velocity in the RPF and that was it...

[vlado]

...The MotionVectors you provided are not in a form we support:...

This is quite wrong; there are a number of threads on the ReelSmart motion blur plugin already, for example this one:

http://www.chaosgroup.com/forums/vbu...ity#post347719

I'm not sure you still have to set the "Vec Scale Y" parameter to -1, you might not need to.

Best regards,
Vlado