motion vector pass and Nuke workflow

[gpapaioa]

After searching the forum, I manged to create a motion vector pass and according to some posts, in order to use it correctly in Nuke, the values must be fitted/normalized. I used MV2Nuke (http://www.nukepedia.com/gizmos/colour/mv2nuke) but still cant seem to find a proper workflow. Has anyone came up with some solid workflow on how to proper use Mantra's motion vector pass? Thank you.

[Neil78]

I use this technique - transferring to screen space - check it out.

 

You could normalize the motion vectors in Houdini - but also MV2Nuke works well for this, as it means that when using the vector blur in Nuke - the 'multiply` value makes sense - such as 0.5 for 180 degree shutter etc.

 

I'd be really interested in any other techniques you might come up with. But also I think that the motion blur in Houdini is so fast, more often than not motion vectors are not always needed in Nuke.

 

motionvectors.hipnc

[Guest tar]

I use this technique - transferring to screen space - check it out.

 

 

 

Isn't shops calculated in screen space automatically? 

[gpapaioa]

Thanx Zweger, I will check your .hip. The thing is that I have to deal with scaled cameras (dont ask why...) and I want to be able to tweak the values in Nuke so I can manually fix them in a way. When you use MV2Nuke, which one do you think  is the appropriate preset for Mantra?

[Neil78]

Hi Marty - good point - i  didn't know that, i'm assuming that 'P' is not - so overcompensating perhaps - but i've never actually tested the difference.

 

gpapaioa - i've found 'raster space' to be best - getting normalized values into vector blur.

[eetu]

Isn't shops calculated in screen space automatically? 

 

To be precise, shops are calculated in camera space, not screen space - and Neil is transforming from camera ("current") to screen ("ndc") space, which looks correct to me.

[Neil78]

Good to know - thanks eetu; i remember finding recently that P was not world P but camera P.  - and thus great for Z depth pass in Nuke.

[gpapaioa]

Thanks everyone for the valuable information 

[XRM]

For scaled cam, I always use an expression in respective scale xyz fields

origin(opinputpath(".",0), "", "SX") 
origin(opinputpath(".",0), "", "SY") 
origin(opinputpath(".",0), "", "SZ") 

 

Check this link http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&p=142497&sid=55ff675427276bd80c80b160b13f1d5f