2D Motion vector from Houdini?

Hello !
Sorry if feels like double post, I longly hesitated to continue the motion vectors thread or start a new one, but since it’s quite houdini , I didn’t wanted to flood the other thread. :thinking:

SO ! since Houdini 16.5 release an intriguing feature has been included, Volume Optical Flow ! I didn’t see any talk or tutorial about it, maybe this is not reliable for game need ?

I tried to generate motion vector from a flipbook animation. I’m slowly getting there but my math skill and Houdini’s knowledge hitting a wall now.

I know they could be generated with the gamedev toolkit but I want to use 2d source for all my flipbook need , like more motion graphics stuff ect.

As you can see I’m almost there (kinda?), but few things are off, It seem my vectors are flipped somehow and don’t errr spread enough ?

Here’s my hip file, hope you don’t mind some of my math/logic foolishness.
Hip file

Thanks :slight_smile:

PS : As @Partikel mentioned below, I based my experiment on this great tutorial https://vimeo.com/242373845


Bare in mind, in Slate I’m doing other options too, so it’s difficult to aim for that as a ground-truth if you haven’t got those. FWIW you could get your houdini output, in Slate, with the correct settings. So I’d say you are pretty close. It kind of looks like a search distance setting, where the Houdini version is tighter in your example. If you can expand the search range you’d prob have quite similar.

It all comes down to preference as there’s not really a “correct” way to do them

Your vectors being flipped isn’t a big deal, it depends on the target.

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Just adding in the Mark Fancher Tutorial for others to see. I’m guessing it’s what your stuff is based on. I think he does a good job of explainig the O flow node.


Indeed ! Forgot to add the reference, my bad.

Has anyone had any luck with this method? I tried it but couldn’t get vectors that are usable in our engine. Like Alex mentioned it does seem that we are missing a few extra things in the volume optical flow node that are required to get this working properly.

I’d rather do this in Cops or after the textures are rendered as I prefer not to spend the extra time re-timing my sim after the original sim.

Hello !
Sorry for pretty late reply, its possible to have working motion vector but its a bit tedious.
You will need to render on a plane thoses motions vector with GameDev simple baker and then make them usable in a cop network.

Also be sure you save your texture in gamma 1 !
Dont do like me realising I didnt export the texture correctly 2 days after :stuck_out_tongue:

I ended up using Slate except for a few cases (when I’m not using flipbooks).(https://www.facedownfx.com/)

Hope that help :slight_smile:

Hi meta_t,

This is really cool, but would you be able to explain in a bit of detail what calculations are going on in the vopcop node?