Motion Blur G-Buffer Problem

[Gonzaga]

Hi ... I have an odd problem concerning motion blur and velocity channel in RPF files.

I rendered a spinning plum and saved the object velocity with the RPF file. After having applied the motion blur within combustion I noticed strange artefacts in the images which make the border of the plum rather frayed. When I checked the G-Buffer velocity channels I saw that there are isolated colored pixels at the edge of the geometry that might cause the problem. They seem to miss some antialiasing.

Here's an image to better illustrate what I mean ... on the left the image with the applied Combustion-MB ... on the right the G-Buffer from the RPF file. Zoom in for better seeing the pixels I'm talking of.



Hope somebody can help ... Regards ... Andreas.

[Gonzaga]

Nobody got answer to this problem? Vlado, where are you? Or do I have to assume that this is a bug?

Maybe somebody can help ... Thanks ... Andreas.

[dimo]

Hi,
Do you have the Object Velocity option ticked in the vray g-buffer rollout?

[Gonzaga]

Hi Dimo ... thanks for the answer ... yeah, I've checked "Object Velocity" ... otherwise that image on the right wouldn't be visible at all and the faulty motion blur would not have been calculated.

Maybe somebody else can help ...

[Da_elf]

i wouldnt think that 2d post motion blur wouldnt lend itself well to something thats spinning like that.

[Gonzaga]

Hello Da_Elf ... the Post-MB-Solutions works fine for me ... it's just that it looks very bad as long as this pixels are wrong ... in frames where there are no wrong pixels the MB is really fine ...

Regards ... Andreas.

[Dynedain]

The problem here is that extra information channels like velocity aren't anti-aliased. This is actually a "good thing" becuase otherwise, the anti-aliased pixels would be a different color, and hence would blur differently.

What you need to do is bring in the coverage channel as well.

[Gonzaga]

Hi Dynedain ... I hoped there is a way to have an antialiased velocity channel ... but I'll try the coverage thing now ...

OK ... I've saved the coverage channel along with the rpf ... now I just need to know in which way I have to use the coverage channel in Combustion to get a better result ...

So Dynedain (or someboby else) ... maybe there's a little hint for me ...

Greetings ... Andreas.

[Dynedain]

OK ... I've saved the coverage channel along with the rpf ... now I just need to know in which way I have to use the coverage channel in Combustion to get a better result ...

I'd like to know too

I've been told coverage is what is used to deal with this kind of issue. All kinds of other channels have the same kind of problem.

[Gonzaga]

Well ... seems as if VRay + Combustion Motion Blur is just impossible to combine properly ... too bad ... that would save me a lot of render time ... maybe the VRay-team will find the time to provide some sort of solution to that problem one day.

Thanks Dynedain for trying to help ...

Greetings ... Andreas.

[vlado]

A quick work-around for this would have been to render the velocity channel with the scanline renderer, but use the original V-Ray rendering as the rgb source.

Best regards,
Vlado

[Gonzaga]

Thanks Vlado ... I'll give it a try ... and I bet a solution for this situation is already on the wishlist ...

...Andreas...