Retiming of rendered images within Max and Vray

[Robert1977]

Dear all,

I am looking for a proper way to retime footage that is rendered out of Max with Vray without any artefacts. Retiming for me is necessary if I render out at a frame rate of 25fps and want to retime it to 30fps to display it on a beamer infrastructure.

There are tools around that do this job like Fusion Dimension or Revision Twixtor, but these tools require lot of adjustments that are not valid for all images of a movie and you always have artefacts in the images here and there.
I have looked into the vector images that both tools generate and they are quite different from the velocity images that 3dsmax or vray can generate.
The velocity vector images that dimension and twixtor generate look like painted images, while the ones from max have sharp edges/borders around geometry. Feeding these velocity images into dimension or twixtor doesn't work, even if I blur them or blur the rgb-channels of the footage.

From my opinion it would be a great feature within Vray to render out a velocity channel that is capable of being fed into the vector channels of dimension or fusion, so in theory, no artefacts should occur anymore when using these retiming plugins.

The velocity channels from vray and max work great for motion blur, but obviously not for retiming (or i am missing something). One issue is that the velocity on a fixed plane is 0, while in a velocity channel from twixtor it has some velocity, if a cube slides over the plane.

I will post examples of the velocity channels here.

[vlado]

I have no idea how to generate such a channel; if you have a link to a technical description (papers, documentation etc) it will be helpful.

Best regards,
Vlado

[instinct]

Actually the "blurriness" is unintentional i think because these tools are analyzing the image not on a "per pixel" basis, but rather on a "per block" basis, with the blocksize beeing different or user defined. And because you do not get pixel exact velocities with optical flow algorithms you end up with blurriness/smoothing i think. If you want to do things right you can render at different FPS from max and you'll get a perfect result. Of course that needs a lot of rendertime.

Regards,
Thorsten

[Robert1977]

Dear Thorsten, dear Vlado,

I have added some pictures showing the different velocity channels from Max/Vray and from Revision Twixtor. Since rerendering the whole sequence at a different framerate is not an option for our large scenes, I would like to investigate further in the topic of retiming.

I think that the "blurriness" is not just because of the analysis on a per block basis, but also because the velocity edges between a fast moving object on a fixed floor or between objects that have different distances to the camera need to be with a smoothly blurred out, with a transition between them, even if you have motion blur applied on the rgb-image.
So the algorithm in twixtor or Kronos from AE enhances the objects corners towards the motion in both directions (forward and backwards), analog to the motion blur on an rgb-image, but stronger and more defined.

So the velocity color for a seat has always more pixels towards left and right, if the seat moves across the camera.

The enhancement is even stronger if there is just one simple cube moving across a floor. The whole image has then almost the same velocity encoded in a pixel, there is no hard edge between cube and background.

[Robert1977]

Twixtor Vector create (next vector), blue = 0.0, max displacement 100:



Twixtor Vector create (previous vector), blue = 0.0, max displacement 100:



Vray Velocity (next vector), blue = 0.0, max displacement 100:



3DS Max Velocity (previous vector), blue = 0.0, max displacement 100: