Hi,

I asked this around on cgtalk but haven't got any response yet. So here goes (and my first post here!).

I'm trying to help the FX team and we need to match up Houdini>Mantra/prman motion blur with Maya/RMS>prman motion blur for hold out reasons and so far have found that Houdini only seems to render sub-frame motion blur. Is there a way where I could only render integer frame motion blur?

Cheers,
Sachin

Not sure if matching motion blurs works, and also not sure that I understand your question. But the shutter time parameter on the camera node controls how much motion blur there is. Set this to 1 and you will get a full frame's worth of motion blur.

Best wishes

Peter

Great to have Peter Quint reply to my first post! Thank you for the invaluable lessons on your Vimeo page.

Apologies if I wasn't clear enough. I debugged the issue by exporting a rib from Houdini and found that for “Trailing Blur” at Shutter Time 1 and for frame, say, 110 it was exporting the motion data from frame 110 to 110.5 (I cross verified by manually moving the frame ticker to 110.5 and the transformation values matched with what was exported). I tried various permutations but Houdini always seemed to sample at fractional frames instead of exporting from 110 to 111.

The equivalent settings in Maya/RMS are Shutter Angle of 360 (for shutter time as 0-1), Frame Open and sampling at “Frame” instead of “Subframe”. That samples shutter open at 110 and close at 111. If I switch to Subframe then the RMS render matches Houdini's. So I think Houdini is always sampling subframe motion blur.

It terms of hold outs I would render Deep maps from the camera for your hold outs. You can render them natively out of Houdini and use them in Nuke. I will go as far to say they are awesome !

Rob

Hi Rob,

I did think of the DCM workflow but never got around to trying it. Does Nuke support rat files out of the box now or do I have to use rat4nuke? Do you have any tips or resources that can help me explore this workflow?

I believe there is a control on the motion blur settings of the Mantra ROP to determine if motion blur is trailing, leading or centred (I don't have Houdini right now). If you set it to trailing, with a shutter time set to 1, you should get motion blur for the full frame.