Wheels - motion blur noisy - looking flat

[Furnace]

Hi all,
Doing an auto animation, as my wheels turn they seem to loose all depth, look very flat, any ideas on how to get the depth back?

Also the motion blur is very noisy/grainy, ideally I want it completely smooth, the samples are set to 36, even if I up them to 128 it's still just as noisy.

Thanks in advance for any help.

[joconnell]

Which samples are set to 36?

You've two factors in motion blur, Anti aliasing and geometry samples. I'd suspect you've got your geo samples set to 36 rather than your aa. Geometry samples are the amount of position / in between / breakdown samples that vray takes for the object. Say you've got a box that rotates 90 degrees over one frame. If you've got 2 geometry samples, vray will look at where the verts of the object start (0 degrees), and where they end (90 degrees) and blur along this line - 2 samples gives you a linear blur between the two positions. If you go to 3 samples, vray will now sample three positions - 0 degrees, 45 degrees in the middle and 90 degrees where it ends - instead of your straight line between the two positions, you'll get a more triangular shape. 4 samples is four positions so 0, 30, 60 and 90 degrees - you'll start to get something resembling an arc in the shape of the blur now. For your wheel you can gauge it by how fast it's rotating, I'd say you'd need maybe 8 - 12 and you'll definitely have something smooth.

On the noise, the major thing here is your max AA and your noise threshold. For anything regarding shape / silhouette / geometry, this is all to do with camera or anti aliasing rays from vray - the more that vray can fire from the camera view, the more accurate it's description of the shape of your geometry is. If you've got a totally static object, pretty much every ray from vray will hit it and you'll get pretty smooth results right away. If you've got something moving across the screen or rotating quickly though, it's almost as if it's in multiple positions and then all of these positions are blended together afterwards. Say you've got an object that starts on the left of the screen and moves to the right over one frame - it'll pretty much be a smear. Vray's camera rays are fired into the scene and will try to hit our object. Now since with motion blur we're adding in a time aspect to our render and trying to sample the object as it moves across the frame, there's a possibility that some rays might miss our object, as it's travelled past the pixel our ray is firing at. To counter this we've got to fire lots more camera rays into the scene and to do this we've got to increase our max aa subdivs. What can be handy at this point is to use the vray frame buffer and add in the sample rate element. If you start off with aa or 1 / 24 it'll be a decent amount for a lot of scenes. If you view the sample rate element after doing a render, it'll show you what aa was used in the frame. Light blue means minimal aa or 1 in our case, red means it's hit the top amount of aa or 24, then green and orange mean middle levels of aa. If you get no red in your same rate at all, it means nothing has used your top aa. Say you're using 1 / 24, you've got no red in your sample rate and the render is still a bit noisy, this means the quality level you've asked vray to work to (or the noise threshold) isn't fine enough. If you turn down the noise threshold from it's default 0.01 to something lower like 0.005, you'll force vray to work to higher standards and your render will get far smoother at the expense of render time. Again look at your sample rate and you might start to see some more red pixels appearing where it's starting to use your max aa values.

Hope this clears some things up!

[Furnace]

Hey, many thanks for this, trying it out now.

Appreciated.