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Where is Twixtor Shake Documentation?

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Will MacNeil
Where is Twixtor Shake Documentation?
on Oct 23, 2009 at 9:59:14 am

Hi, I'm having a tough time trying to use motion vectors in Twixtor Shake. I can't seem to find the manual (which is supposed to appear after install - but I'm not going to install again just to find it.)

Here's what I'm trying to do:

I've got a 3D scene rendered out. It's 30p. I need it to be 29.97i (or 60i, I suppose.) So I've taken it into Twixtor in Shake and set the speed to 50 percent. I then take this into FCP and change the speed to 200 percent with Frame Blending on. This is a method suggested by Marco Solorio here on the Cow.

This is working well aside from the motion artifacts I'm getting from Twixtor. So I thought I'd just bring in the motion vectors as these are easy to render. But I'm not sure how to format them properly and the Shake tutorial scene is not that easy to reverse-engineer.

Are there tricks to using motion vectors here?



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Peter Litwinowicz
Re: Where is Twixtor Shake Documentation?
on Oct 23, 2009 at 6:20:49 pm

Motion vector format info is located here:

You first need to render out your motion vectors from the 3D program you are using. Info you need is here: Click on the blue bar for the application you are using. The various tutorials talk about ReelSmart Motion Blur, but the same information is to be used for Twixtor.

Then, with the displacement setting you use, assign Twixtor's motion vectors to that sequence. Depending on the application, you might need to flip the Y component by setting the Vec Scale Y value to -1. Then you'll need to set these vectors to the InputPrevVectors or InputNextVectors as appropriate (that is, whether the motion calculated to the prev frame or next frame by the 3D system).

note that you'll want to perform the retiming on each object individually, because as objects cross the motion vectors will cut the motion distinctly along the objects' silhouettes if you do this will all objects in the scene at the same time (your mileage may vary: retiming all objects at once can also look good depending on the scene composition).

Pete Litwinowicz
RE:Vision Effects, Inc.

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Pierre Jasmin
Re: Where is Twixtor Shake Documentation?
on Oct 23, 2009 at 7:29:11 pm

Actually x scale might need to be -1 as well
The best is to animate a simple rectangle and animate it so the speed is different at each frame and play with scale x and y +/- 1 so it matches - and try the 4 -1 or 1 x and -1 or 1 y... to see which one is the right one.

I know for example with the same mental ray renderer Softimage is to previous frame and Maya to next frame. And if you use MR production shader or LaMaison it's different. LaMaison is scaled flipped -1,-1...


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Pierre Jasmin
Re: Where is Twixtor Shake Documentation?
on Oct 23, 2009 at 7:31:31 pm

Also if the 3D animation motion is to previous frame there is no motion on first frame (so you might need an extra frame before).

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Will MacNeil
Sorry, I'm just not getting this
on Oct 26, 2009 at 12:20:37 pm

Thanks for the help, guys. But I'm still a little lost. I'll try to break down my question:

I've rendered a scene out from C4D. It's several flat objects moving over a static background. I want to run this shot at 50 percent so that later I can speed it up and generate an interlaced file.

Please let me know if I understand this correctly:

I should render out one pass of motion vectors from C4D (I'm using R11.5)

This should only include the moving objects. The static objects should not be included in the vector pass.

Twixtor will then create its own alpha based on the vector pass(?) Or do I need to import a matte for this?

I also need to determine whether C4D renders out vectors looking forwards (next frame) or backwards (previous frame) (?)

And finally figure out whether these are in positive or negative spaces in relation to Twixtor's setup.

I only need to fill in one of Twixtor's vector inputs?

Thanks for your help,


Will MacNeil
Film Editor

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Pierre Jasmin
Re: Sorry, I'm just not getting this
on Oct 27, 2009 at 4:39:04 am

In general the Motion Vectors need an alpha channel
About: C4D Object Buffer

Your color/beauty passes should be RGBA as well
If an object is not semi-transparent the MV could share the same alpha
(these alpha channel assignment mean precomp in AE)

You can only generate from CG one direction of motion and you need to figure out with C4D if the motion goes forward or backward (no idea) - so leave the other off (NONE) in twixtor


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