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Clean Motion Vectors

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Hayden Martin
Clean Motion Vectors
on Oct 15, 2014 at 4:55:50 pm

Hi guys

I'm having a tough time getting my motion vectors crisp enough so that they don't cause weird artefacts or clip when I bring them into AE for vector blurring.

How can I tell if my vector is 'clean' and ready for post motion blurring fx?



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Cassius Marques
Re: Clean Motion Vectors
on Oct 28, 2014 at 1:16:54 pm

I think the recommended values will vary from plugin to plugin... there are some things you can do like render a higher resolution and let AE scale it later... but I think it will never be perfect since you can't apply accordingly in-between values on edges.

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Hayden Martin
Re: Clean Motion Vector
on Oct 29, 2014 at 3:28:36 am

That's some great feedback

It's interesting to know that edges and other variables come into the equation.

I'm only working with r13 at the moment... Do you mean to say that there are better motion vector pass plugins for C4D? If so what are they? So far I have only used the built in pass to be utilised in post by RSMB Motion Vector Pro in After Effects

I'm using 16bit PNG images for better motion vector depth, but 32bit PSD files take up too much space when arranges in an image sequence... (2000x2000px .PSD = approx 32Mb image file size)...

Is there another reliable codec / format that can save my motion vector passes in a more reliable format?


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Eric Bowman
Re: Clean Motion Vectors
on Dec 22, 2014 at 5:09:44 pm

I know this is fairly old now, but I thought I'd leave this here in the event someone has the same problem. I recently used RSMB for a 3D animation and had a heck of a time getting overlapping 3D objects to play nicely. Basically if one area of the 3D mesh were moving in front of another mesh, it would not be blurred. The correct fix would be to have a render pass for the foreground element and another for the background. This would have required many hours of re-rendering however, and I didn't have the time.

So, I then found the following two links:

The gist is:

1) BEFORE you render your beauty/RGBA pass, add a multipass item in Render Settings for the motion vector pass. This will save a separate render pass just for the motion vectors.
2) Per RE:Vision Effects page, you SHOULD be using an alpha. Anything transparent will not be calculated resulting in a much better blur.
3) To get rid of the sharp edges when you apply RSMB Vectors plugin to your RGBA pass, precompose the motion vector pass and the RGBA pass together. Place the RGBA on top of the motion vector pass and set the motion vector pass to use the RGBA pass as an alpha matte.
4) Use simple choker on the RGBA layer that is above the motion pass, and set it to roughly 2-3 pixels. This will choke and soften the alpha a tiny bit, ultimately resulting in a better motion blur.
5) Place that precomp into another comp, slap the original RGBA pass on top. Add the RSMB Vectors plugin to the top RGBA layer and point the plugin to the motion vector precomp. You should notice a much nicer result now.
6) Finally, you might need to go to the motion vector pass in the Project panel, right click > interpret footage > color management and click on the Preserve RGB checkbox.

Another tip:

For my project I didn't have time to have two passes rendered for my foreground object and background object. I first tried the RSMB basic plugin and it did a pretty good job. The RSMB Vectors plugin was much more accurate after some tweaking, but I still had an issue with the 3D object overlapping and where they did overlap I had no blur. It looked bad. So, I added the RSMB Vector plugin first, then right below it I added the basic RSMB plugin with a very low setting of .25 for the amount. By adding the RSMB plugin under the RSMB Vector plugin, it blurred everything a little further and allowed the overlapping areas to blur.

Thanks for reading my book. ;) I hope it helps someone.

Eric Bowman

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