motion blur in empty area

[Felix2]

Hi,

how does vray motion blur work? I noticed that it slows down the hole image area calculating even the empty area where is no objects. what is the reason for this? is there any change to detect or something so that vray could know where the objects are? Im just wondering and of course this would be nice feature

[instinct]

It does so because BEFORE sampling with motionblur VRay doesnt know yet if there is an object or not. Imagine a car moving quickly from left to right. Now right in front of the car there is no car without motionblur, and only when taking motionblur into account it is visible. I guess there could be some "Boundingbox with Safetyarea" thing done, but i am not sure how good that would work (esp with moving cameras AND objects things can go whack)

Regards,
Thorsten

[vlado]

You can try to move the sampling from the motion blur to the AA, e.g. use DMC aa with 1/6 subdivs, and leave the motion blur subdivs to 1. This will make the rendering of empty areas a lot faster, since V-Ray will only take 1 sample per pixel there.

Best regards,
Vlado