I'm animating the rotation of a truck's wheels, and they have a clearly visible tire tread. Everything works, but I'm getting a severe case of the frame-rate aliasing problem which means that at certain speeds my tires appear to be rotating backwards, or slowly, or even not at all. It's bad enough that I'm not sure I'll be able to deliver a movie that would help people to understand our technology.

My keyframes are designed to show the truck accelerating from a standstill, then decelerating to a standstill, so I run through a wide range of rotation speeds.

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I also have rotating gears in a gearbox, and the problem's bad there too. Teeth, you know...

I understand why this is happening (periodic geometry advancing spatially but sampled at the frame-rate - it's a temporal aliasing thing)... but I'm wondering if anyone has come up with any methods for mitigating its visual impact. Note that I'm observing this in the 3D window. I haven't yet tried rendering a movie; but I don't expect I'll escape the problem in the rendered output.

Any wisdom?

Would motion blur help?

  • 4
    $\begingroup$ Motion blur would almost definitely help. This is also a phenomenon that takes place in real life due to camera frame rates - a popular example is youtube.com/watch?v=R-IVw8OKjvQ $\endgroup$ – Ronikos Dec 22 '16 at 19:48
  • $\begingroup$ The phenomenon is called stroboscopic effect and also happens to real cameras (e.g. helicopter rotor in a movie). Motion blur is certainly an option, since this is what our brain does (the spinning rotor looks like a transparent disk). The effect can also be seen by the human eye if a light source illuminating a moving object is flickering very fast. $\endgroup$ – user2859 Dec 23 '16 at 10:53
  • $\begingroup$ Don't worry - I know all about the stroboscopic effect. And about time-varying light sources... I wrote the book on the topic. :) Take a look at timevaryinglights.com. My question was what can be done in Blender to mitigate it. $\endgroup$ – Dan Bennett Dec 23 '16 at 15:33

Motion Blur would be my answer for a good reason! If you blur something it will appear moving. Also Its like in real photography, if you are using cycles you can set a value for the shutter. set it to something around 0.8 to achieve best results. In real movies the wheels actually also appear moving backwards. You could do a slow motion. Or you could try to higher the framerate.

  • $\begingroup$ Yes, I"m testing it now. I rendered my movie without motion blur, and now I'm rendering it again with 0.5 shutter time, which I chose because I'm a videographer who likes the 180-degree rule. :) I'll see the result when I get into work tomorrow morning. $\endgroup$ – Dan Bennett Dec 22 '16 at 22:38
  • $\begingroup$ Motion blur helps a lot. Thanks! I'm going to increase it to 0.8 (she cannae take any more, Captain!) to see what that looks like. $\endgroup$ – Dan Bennett Dec 23 '16 at 15:34

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