View Full Version : question on exporting motion vectors from mental ray to nuke

10 October 2009, 05:32 PM
Hi guys,

I have been trying to export motion vectors from 3ds max to nuke. I have tried the p_motion_to_rgb shader numerous settings(raster space, camera space, reelsmart) raster space is supposed to be the solution! but it doesn't seem to work.

I have tried with the velocity pass in render elements and/or motion blur on with 1 sample to force the motion vectors into the buffer.

Also tried max 2010 connection extensions mental ray velocoty frame buffer saved to exr files (rgb,rgba,xyz,xy,uv) to no avail.

Has anyone been clever enough to get the right vectors into nuke?

many thanks,


10 October 2009, 04:29 PM
what are the settings you are using in Nuke?

Dont use Max but in Maya the present entitled 2dToxik Motion Vector seems to work pretty much as expected in Nuke provded you set vector blur correctly.

10 October 2009, 07:54 PM
Thanks for the reply Aneks,

I have finally solved the problem:

when rendering in 3ds max with gamma correction 2.2 you need to put an mi utility gamma correct onto the p_motion_to_rgb shader and any other shader render passes like Ambient occlusion etc. I would imagine it's the same n maya?

also you need to have a velocity pass in the mental ray exr framebuffers active for the motion to be created in the p_motion_to_rgb shader. I set this to half float and uv, not sure if the mode makes a difference.

the p_motion_to_rgb was set to reelsmart and I normalized at 1, rendering half float.

However I really love the new connection extension for 2010, finally multipass rendering in exrs with mental ray!!

10 October 2009, 11:34 AM
In Maya if you tell mental ray to use a floating point format like .exr and set framebuffer gamma to 1, which it is set to by default, there is no need to add any other colour corrections.

also be aware that if you are using multichannel .exr in Nuke then it will only apply the colourspace conversion of a read node to the RGBA channels and not to any additional channels on the image. This is probably a good thing as you would want to be using linear .exr anyway not sRGB and sticking additional channels.

CGTalk Moderation
10 October 2009, 11:34 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.