Heavy Vray Problem with Motion Blur

[Thomaskl]

Well, i just experienced a nice bug in the motion-blur feature. Link a sphere to the camera and move/animate the camera with high-Speed through your max-universe. Take a look through your camera at the sphere. While you have no relative movement between camera and sphere, the sphere becomes heavily blurred when rendered with Vray-Motionblur.
It although happens when you animate both objects paralell to each other without linking.
And i think i found another bug concerning this, in connection with groups.
Please take a look at this, becaus i cant render the stuff which comes from animation department. The guys will kill me, if i tell them, that i cant render these animations.

Regards,
Thomas

PS: Using Vray 1.47.03 in Max7.5

[joconnell]

Okay this isn't a fix of course but it might get you through this one case -

Make a new maxscript and paste the underneath code into it. Go File > evaluate and you should have a little floater.

Use the "Object to track" button to pick your sphere that is attached to the camera. Set a start time and a stop time for the track and then hit the "Track Object" button - it'll make a copy of your object, run through the specified range of frames and bake the position and rotation of the object into keys.

rollout ObjectTrack "Object tracker"
(
	PickButton TrackObj "Object to track" align:#right width:200	
	spinner Starttime "Start Time" align:#right type:#integer range:[-10000,10000,slidertime]
	spinner Stopttime "Stop Time" align:#right type:#integer range:[-10000,10000,slidertime]
	Button track "Track Object" align:#right width:200 enabled:false
	
	on TrackObj picked obj do
	(
		TrackObj.text = TrackObj.object.name
		global TheTrackObj = TrackObj.object
		track.enabled = true
	)
	
	on track pressed do
	(
	
		if (TheTrackObj != undefined) then
		(
			undo on
			(
				animate on
				newObj = copy TheTrackObj
				
				newobj.name = (TheTrackObj.name + "_copy")
				newobj.parent = undefined
				newobj.wirecolor = (color 30 255 0)
				
				animate on
				
				for t = Starttime.value to Stopttime.value do
				(
					slidertime = t
					newObj.transform = TheTrackObj.transform
				)
				
			)
		)
	)
)

createdialog objecttrack width:300

[Thomaskl]

Thanks for your quick response, and that script...

But i think it is a generall issue within the motion-blur algorythm. I dont have a sphere to render at all Was just a little example. The Szene, i have to render is a little bit more complex, with many objects linked to each other and a lot of animation controllers....So, a little workaround doenst fix the general thing.

Please ChaosGroup Team, take a look at your programming and tell me, why these things behave like they do now...

Regards,
Thomas

PS: in my special case, it has a big effect on the speculars and reflective features of the material. When the materials are rendered with no MB, i have a hot and powerful spec, and with MB set to Duration 0,001 there is nothing left from this specular....

[joconnell]

I'm going to expand this to more complex such as multiple objects / controllers so it might become more useful in the future. I've never tried linking anything to the camera personally so I've never seen this - never had problems with motion blur using parenting or constraints though - weird...

[dimo]

Hmm,

just checked. It's indeed blurred. Not as heavy as if the camera is not linked at all but still visible. Boosting the geometry samples helps but of course not in a complex scene. I remember we had similar problems because the shadows got blurred over the object. I think this was considered as "not implemented" instead of "bug". Perhaps I can find the thread... So if the camera bug is fixed you still have the problem with the shadows that get blurred over the geometrie...

It sounds like your scene is too complex to "translate" it into camera space? (So the whole scene is moving around your camera)
I used a similar technique to render VRayProxies with motionblur.

Best Regards,

Dieter

edit:

Thread found:
http://www.chaosgroup.com/forum/phpB...ic.php?t=11514

[vlado]

Thomas, what kind of motion blur are you using? V-Ray's own 3d motion blur or a Motion blur render effect?

Best regards,
Vlado

[vlado]

It probably doesn't help much, but you get the same error with mental ray when the motion segments are more then 1.

Best regards,
Vlado

[vlado]

In my simple test, the fix was to go the V-Ray properties of the "sphere", uncheck the "Use default motion blur samples" option, and set the "geometry samples" option below it to 3, while leaving the same setting in the Render Scene dialog to 2. If this doesn't help, maybe you can send a simplified scene so that we can look at it here.

The source of the problem is that for the camera, V-Ray takes one additional keyframe at the middle of the frame, while this is not done for the objects in the scene, which causes some mismatch.

Best regards,
Vlado

[Thomaskl]

Hey Vlado,

Thanks for your respone. Nice to hear, that MentalRay got the same problems
As already mentioned, more geomtry samples do change the motionblur, perhaps reduce it to a minimum, but the problem is still there.
mmmh..I am currently trying to translate the szene into Cameraspace. Well, i got it for one szene now, and it works quite well. I instructed the animators to avoid these problems in future szenes. But i think it is a general issue in the algorythm, or ?

Well, i think i can manage the thing by now, but "even" if mental-ray cant do this, it would be cool, when vray would be able to do !

Thanks, so far !

Regards,
Thomaskl