correct usage of motionVectors and vectorBlur

[alexB]

hi,

i am just trying to figure out, what the correct usage of maya rendered motion vectors and the vector blur could be.

in a first simple test i just made a sphere and moved it to the side.
the result was not good and looked like this:


after reading this:
http://www.vfxtalk.com/forum/lm-2dmv...73.html?t=9773
and especially the last post, i turned the "Alpha" on, and the image looked perfect.

so i thought it would work.

then i rendered another test and now all fails again. first without the "Alpha" checked:

nothing i can use as before.

then with checked alpha:

o.O terrible

does anyone have an idea?

btw: the motion vector pass is rendered from maya 2009 with the new preset, which outputs r and g as float values for x and y (toxic style)

cheers & thanks

alex

[hugo_guerra]

Try blurring or grading the vector pass, sometimes it helps.

Also I found that from Maya it is a lot more accurate using the LM_2DMV shader, try it.

http://www.fxshare.com/nuke/download...olor/4428.html

Regarding what Torbjörn said in another motion pass thread early:

http://www.vfxtalk.com/forum/learnin...ay-t17009.html

He is right, it is a cool way to make the MB look almost like a 3D MB.
It is pretty easy to import the geometry and the camera and using the 3D scene to render a motion pass, it is very slow to use this technique during comp, but I usually render out as a pre comp only that motion pass as a float .exr seq, then I import it to the scene and use it just like a vel pass. The cool thing is that this way you can also have the motion pass of any new graphics you may have put in the 3D system of Nuke, so you get a merged motion pass, with both the geo and the new stuff.

Hope it helped

[alexB]

hi,

to blur the vector pass was an idea that looked kinda ok, but i was unsure of that procedure.

i just downloaded the LM_2DMV.gizmo and i am gonna give it a try.
i guess that one expects another format of the motion vector data. using the according maya shader is not really an option anymore, since i would like to use the built in ones from maya rather than others.

the 3d import is a real funny idea. i really have to think that way
nuke is my first compositing app with 3D space. gona give it a try.
but to be honest: usually our scenes are to big and hold too many objects to work that way. defining a material for them all will take ages i guess.

but thanks a lot for the infos so far. i keep on checking.

cheers

alex

[hugo_guerra]

Sure, I always use this technique in small scenes, that is true.

But you don't really need to change materials, since you only need to export the entire scene in FBX or Obj from Max and you don't need to do anything except output the motion pass created by the scanline renderer of Nuke.

I does take time to load the first time in Nuke, but once the FBX or geo is there it is pretty fast to work. and I suggest leaving in a farm or during the night the motion pass render, don't make it in the "fly" in the comp, that is just too slow.

Just pipe a black Constant to all the geo and use the shuffle to bring the motion pass to the RGB pass of a write node.

[Diogo Girondi]

Can you post a frame of those so I can take a look at the mv pass from Maya?

[alexB]

hi,

i attached an exr with a toxic style (r and g) and a normalized motion vector pass inside.

sorry. the non animated persp camera sneaked in as well

cheers

alex

[hugo_guerra]

I try it now, but where is the camera going to, which direction? Since I don't know if it is correct now.

Look at the nuke file, is it correct?

It still looks bad, but maybe be because it is pretty not antialised.

In VRay I usually just put a -1 in the y channel with a multiply node and it works fine, but in Maya I have no idea.

[alexB]

that is basically it but as you see on the left side you get problems
the camera moves (rotates) to the right

cheers

alex

[hugo_guerra]

I see, it seems like a edge problem, I had this in VRay also.
I always try spliting my objects in several renders to get several of motion passes to control better the blur, since this is happen because there is no information in the image to make a correct transparent blur in that small areas.

Try rendering the floor separated from the pilars and render the front pilars seperated, that way you can control the blurs a lot better.

It could also work better by using the geo to create a new motion pass inside Nuke.

[alexB]

yes you are right. i guess in that case i have to seperate some of the renderings.

or if all fails: for gods sake render motion blur in maya

cheers & thanks

alex

[debris]

VectorBlur is seriuosly broken in 5.1v2!
I already sent a report to thefoundry and they confirmed that. Will be fixed in the next release.

[alexB]

thanks for that info. that will prevent some serious trial and error from my side though

cheers

alex

[hugo_guerra]

Sorry, I should say that I am using 5.0v2 and 4.8, so the results are still this ones.

[Diogo Girondi]

Thanks Alex!

I'll take a look at it later.

Cheers,

[Denis]

In VRay I usually just put a -1 in the y channel with a multiply node and it works fine, but in Maya I have no idea.

Hi, please can you descripe how you do this. I have the 5.1v2 PLE and no idea how to achieve the effect,
that the "Vec Scale Y"-property has in RSMB as descriped on the Revision website:

IMPORTANT NOTE: 3ds Max renders out velocity images assuming that the y
index for pixels of an image increases as you go down the image, and our plugins
assume that the y index of images increasses as you go UP the image.
As such you will want to use a Vec Scale Y of -1 when using our plugins
when rendering out velocity images from Max 8.