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When the shutter opens on a real motion picture camera, or a video camera, objects that are moving to the frame during the time that the shutter is open become blurred. This artifact is called motion blur and it's huge it making your 3D images look less computer-generated. Now before I get started, I want to say that the effects that I'm talking about are part of the Physical Render Engine, which is built into the Broadcast and Studio versions of CINEMA 4D. If you only have the Prime, you can still get motion blur, but you can't get the physically correct motion blur. The scene I have here is just a bunch of blocks that are falling down and hitting the camera and bouncing off as they come through the frame.
I'm going to park the rendering right about here and let's make this perspective view full screen. Before I get started, I want to talk about the camera, and if I go to the Physical settings on that, the only thing that we're going to be concerned with right now is the shutter speed, and it's at the default of 1/30th of a second. Let's bring up the render settings, Command+B or Ctrl+B, we're going to go to the Render pulldown and activate the Physical Render Engine, and when we do that let's make the Render window quite a bit smaller.
We're going to click on the Physical option. The only thing we're going to be concerned with for this movie is the Motion Blur setting and these Motion Subdivisions down here. So before I activate motion blur, I'm going to hit Command+R in the keyboard or Ctrl+R on the PC to render the active view, and then I'm going to turn on Motion Blur, and when I do that, I'll hit Command +R or Ctrl+R again, and you'll see that nothing really happen, that's because the motion blur effect is not previewing in the editor window. I have to do a render to the picture viewer to actually see that effect, so I'm going to go Shift+R on the Mac or Shift +R on the PC, and that's going to bring up the Picture Viewer.
Now I have some stuff preloaded in here on the Picture Viewer, and we'll talk about those in a minute, but this is the current render that we're looking at right now, and you can see that we already have a pretty nice-looking motion blur effect. So this is the default value for the motion blur, we have the default value for shutter speed at 1/30th and we've got the default number of subdivisions for the motion blur in the Render Settings, so this is the default. Let's make this window a little bit smaller, and we're going to go back to the Motion Subdivisions, and we're going to change the Motion Subdivisions from 4 to say 6, and then we'll go Shift+R once again, and you're going to see that it's preparing the motion, and it's going to take a moment to think about that motion and it's going to render the frame.
And now we can compare these two images. Let's bring that a little bit larger and go right back and forth between the two, and you can see that there is almost no difference between those two renders. What this Motion Subdivision is doing is, it's helping CINEMA 4D calculate how objects are moving through the frame. The time where you'd want to turn this up is when you're using objects that are moving in a curved fashion through the frame, like, say for example, a propeller or if I'm waving my hand through the air, my hand is moving in an arc, anything that's moving in an arc is going to need more motion subdivisions than things that are moving in a straight line.
These cubes are moving mostly in a straight line, so we're not seeing the effects of the motion subdivisions, so we're going to leave this back to 4. So now with that set to 4, the only things we're going to be concerned about with are going to be the Sample Quality, and then the Shutter Speed, so let's take a look at the shutter speed. The shutter speed right now is a 30th of a second. The longer the shutter is open, the more motion blur I'm going to get, so let's take this and change it to say 1/8th of a second. Now we're going to hit Shift+R on the keyboard again, and you can see now we have a much more pronounced motion blur effect.
So if I compare that with this first render, this is the first render at four subdivisions, and a 30th of second, and this render is 1/8th of a second with four subdivisions, you can see the motion blur effect is much more pronounced. You see that there is quite a bit of grain going on in the motion blur and that's because of the sampler. Right now, in the Render settings we're using the Adaptive Sampler, which is fine, but you can see that we have it set for low quality, so that we can get a really fast render. If I turn this up from low to high, and then hit Shift+R on the keyboard, I'm going to speed this render up in post, so that we don't have to wait so long for it.
So you can see that rendering took almost a minute for a single frame. If you compare that with the previous render where it was only 8 seconds, you can see that that sampling quality has a huge impact on the render time, but it also has a huge impact on the quality of the render. If we look at the grain, especially in this area here, you see that it's much, much smoother, and this is a very good result. It's the unfortunate fact, the higher the quality render, the longer the rendering is going to take.
I've pre-rendered some different motion blur tests here for us, so that we can see these previews in the Picture Viewer and I've got them already loaded in here and these are QuickTime movies that I have loaded in, let's take a look at these and play them back. So I've got number one here, and I'm going to hit play, when I hit play we're going to see a green bar start to form, I need to let it play through all the way through one time and it's going to cache the green bar. Once it gets done playing, then it'll playback in real time speed, so let's hit play here, and you see it's chunking along there, and those gaps are frames that have not been cached, and so this is the default settings for the motion blur.
Looks pretty good, it's not a bad looking motion blur effect, but it could be better. So the next thing I did was to up the shutter time, so that now the shutter is open longer, still the same number of samples, and I'll hit play and let it cache through. So now you can see we have a much more pronounced motion blur effect, but it's very grainy. So now let's take a look at the additional motion subs, and you'll see that they have almost no impact on the rendering.
Once again, I'll let it cache all the frames, there we go. And lastly is the high sample rendering, this is 1/8th shutter, 4 motion subdivisions, but on high sample quality, and I'll hit play there and while that's caching I'll just take a moment to talk about the render times for these movies. The default movie took about 12 minutes to render, the 1/8th shutter speed took about 14 minutes to render, the 6 subdivisions took 29 minutes to render, but didn't look any different than the 1/8th shutter before it.
The high-quality rendering with 4 subdivisions took 2 hours and 10 minutes, it was a hugely different render time, but it's a much better looking render. So you can see the biggest factor in the render times for the physically rendered motion blur is the quality setting, keep it low for test, and then turn it to high for your final render.
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