Motion blur the motion blur

[Morbid Angel]

Hey guys, Vlado.
Been rendering with vray RC5, not sure if its already fixed. I have run into an issue, where I have rendered some frames with motion blur, but afterwards we felt that motion blur length was not enough, so we thought to use the vector pass to extend the motion blur.
But we learned that vray will output motion vector blank, if motion blur is turned on. If motion blur is off, the velocity output is correct.
We used RC5 and physical camera, but it also happens with normal camera. So basically there is no way for us to reuse the frames which we have rendered, since the motion blurred frames will not match the velocity frames.

[vlado]

Yep, velocity channel is not generated if you have motion blur turned on; a solution might be to re-render the images without any lighting and just default materials to get the velocity channel.

Best regards,
Vlado

[Morbid Angel]

yes, but, since the main frames do have motion blur in them, the velocity pass will never match.
I had this once in mental ray. And lamaison shader generates motion vector with or without motion blur, so we could extend the already motion blurred frames ever so slightly you see.

[Mdelosrios]

I'm bumping this thread because we are having issues with motion blurred velocity passes being incorrect and inconsistent....

Is there a fix for this?

We are trying to use the velocity vectors to clean up some of the motion blurred noise we get on over bright elements

[vlado]

I'm not sure, I have not tried it in a while. Best to test and see what comes out.

Best regards,
Vlado

[Mdelosrios]

Is there a way to map velocity vectors into a texture? Similar to what can be done in Maya woth the sampler info node then?

I guess theother option would be doing the math the recreate the vectores from the back/forw occ info, but I am afraid It will not fully match the beauty render

[vlado]

If you add extra V-Ray attributes to the samplerInfo texture node, you will get velocity and speed outputs, in world space.

Best regards,
Vlado

[Mdelosrios]

Wait, in Max?

[vlado]

Wait, in Max?

Ah no, that's in Maya. But we can add those to the VRaySamplerInfoTex in Max relatively easily if you need them.

Best regards,
Vlado

[Mdelosrios]

Yes... that would be awesome...

Also, I just figured out how to use forward and backward occlusion to generate velocity vectors in nuke, but do you think one could write maybe in the blue, or in the alpha, the duration in frames of the motion blur...
This would help a lot. Or maybe be able to write it in the exr metadata?