View Full Version : Mentalray motionblur problem

01 January 2005, 12:44 PM
Hi, I have this problem with the motion blur in mental ray.
When I have an animated object that suddenly stops, the motionblur still stays on the object. You can recreate the problem if you make a cube and animate it a long distance in 3 frames and create an extra key at frame 10.
Set al the curves to linear. When you render the animation in batchrender you'll see that the motion blur doesnt stop after the cube is stopped. It only happens in the batch render because I think the motion data only get refreshed when a new batch render is started.
I have had this problem in every project I used mental ray and motion blur.
On this forum I read a solution was to tweak the curve so the curve isn't completly linear, but when I have something like a baked simultation or a motion capture animation it is too much work to tweak every curve.
Using the lm_2dmv shader to render the motion vectors has the same problem.
I don't understand I can't find more information about this, because it seems like a big problem for mental ray for maya users.

I hope maybe somebody has a workaround or a solution for this?



01 January 2005, 02:53 PM
i could recreate the problem. lazy.
since i got not much time to do further tests, but like to provide a solution, i would suggest to go the pragmatic way and setup a render batch, which will render your sequence in single frames.

01 January 2005, 02:48 AM
Starting the batch every frame works, but if I have a big scene file it takes a lot more time to render, because it has to load the scene every frame.
I still don't understand why I can't find much on cgtalk or on the web about this problem. Or it must be something I do, that causes the problem.
thanx for the reply.


01 January 2005, 11:15 AM
if you can't figure it out try to do the mb in post. for me it worked perfectly. look in this ( thread for more info.

it's faster and maybe even better...


01 January 2005, 11:30 AM
hey berniek, you should read the posts more carefully.
the problem is with the lm_2dmv shader too - like arjan already mentioned.

Using the lm_2dmv shader to render the motion vectors has the same problem.

02 February 2005, 11:13 AM
Hi, In maya 6.5 the problem is still there.
I have created a maya scene that shows the problem when you batchrender it in mental ray. frame 3 and 4 supose to have no motion blur. If you render it in a window in maya you see that there is no motion blur in frame 3 and 4.
Maybe someone can batch render the scene in mental ray and check if it renders the motionblur the right way.
you can download the file (maya 6.0) here (



02 February 2005, 11:30 AM
hi all,

i cant get any motion blur at all when command line rendering, can anybody help ?


06 June 2005, 12:47 PM
yap i have same problem and only way i have found is:

(you have to write batch file, let's say render_start.bat)

render -r mr -s 0 -e 0 scenename.mb
render -r mr -s 1 -e 1 scenename.mb
render -r mr -s 2 -e 2 scenename.mb

it works this way, and it really sux

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06 June 2005, 12:47 PM
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