Motion Blur with Mental Ray

In this tutorial we are going to take a look at the settings and what they do for us in using Motion Blur with the Mental Ray renderer that comes with 3D Studio.

For this little demonstration we are going to need an animated object. We will go ahead and set this up as we go.

Open up a new 3D Studio scene, and on your create tab, go to Geometry and create a box in your Front viewport.

Draw a box in the front viewport, just so that we are all on the same page when it comes to settings etc.

It doesn't matter what size the box is, as we will adjust them in the Modify Tab next so we all have the same dimensions.

After you create a box, click on the Modify Tab and enter the following values.

A Length of 150, Width of 20, and Height of 2. This will give us a long thing box that we can animate kind of like a propeller.

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Next, toggle on your Select and Rotate tool by pressing E on your keyboard, or grabbing it from the ribbon at the top of your screen.

We are going to animate our propeller turning and use the curve editor to cycle it so that it repeats continuously.

With your rotate tool, select the box we created and then go to the bottom below your timeline and turn on the autokey button.

The Auto Key button will create new key frames automatically for you whenever you move your timeline to a new frame and then move an object in your scene.

Set your timeline scrubber to frame 10.

To get an exact animation, we will animate by using the Location Coordinates at the bottom of your screen below the timeline.

With Auto Key on, and your scrubber at frame ten, put a value of 180 in the Y-axis field and press Enter.

You won't notice a change in your viewport until you scrub back and forth between frame 0 and 10. Then you will notice that we have animated our box rotating like a propeller exactly one half a turn.

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We can use our Curve Editor to make this half turn rotation animation cycle infinitely. Turn off your Auto Key, and then click on the Mini Curve editor button to the left of your timeline to open up the curve editor.

The timeline will change from the normal presentation, to the mini curve editor where we have a lot of animation tools at our disposal.

In the list view to the left of the Curves/Timeline scroll down until you see the Rotation and select Y Rotation to display only the animation for the rotation in the Y Axis.

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Then, drag a selection box around both of the Keyframes at each end of our Green Y-Rotation Curve.

The little white boxes at each end of the solid green line are your keyframes, make sure you select them both.

Then, we will set our Tangent so that the propeller does not use any slowin/slowout at all. Click the Linear Tangent button with both key frames selected. It can be found here:

When you click it, your green curve will change shape, from a rounded flowing curve, to a sharp straight curve. This means that the speed at which the propeller rotates will not slow down or speed up as it gets near the keyframes. Instead it will start up and stop at the same constant speed.

Next, we will use a Controller to make the Animation Cycle over and over repeatedly.4

Make sure you still have both of the Y Rotation key frames selected, and go up to the menu bar at the top of the mini curve editor. In the Edit menu -> Controllers -> Out of Range Types ...

A New dialogue box will open with several choices for making your animations repeat themselves on the in and out of the key frames.

Toggle the In and Out buttons under Cycle.

Then click on the OK button after you have turned them on.

Your Curve will now show the animation starting over again and again and again via a dotted green line on either side of the animation you actually created.

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Click on the Close button to close your mini curve editor.

If you play your animation back, you will see that the propeller now spins full over and over and over again.If you move to frame 13 and take a render you will simply see your box at the current angle of the animation like this...

This doesn't look very good in an animation, and when something is moving fast like a propeller does our eyes or a camera would capture it in a blur. Making it feel as though it is truly moving fast.

This doesn't happen automatically in 3D Studio, but we can simulate this effect using something called Motion Blur.We can turn it on or off for each individual item, as well as tell the entire scene to use motion blur. Customizing this can make a huge difference when animating because we can control how everything looks and feels. We will turn motion blur on for our object only, just so you can see how to do this as in the future you may not want everything to blur, only certain objects.

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Right click on your Box to bring up the Quad Menu, when the menu appears find Object Properties.

The Quad menu houses a quick way to find many useful settings like Hide, Freeze, a quick way to get to your Move, Rotate and Scale tools

Clone an object, or even turn it into an Editable Poly.

We are looking for this gem, Object Properties where we can change a huge amount of settings just for the objects we have selected.

Anything from visibility and display options on over to Advance Lighting options.

Click to bring up the Dialogue box.

In the bottom right corner of the rather large dialogue box on the General tab, we will see the Motion Blur Object settings.

There are 3 choices for types of motion blur that we can turn on or off.

None for no motion blur

Object for a type of motion blur that is added directly to the objects in a scene.

Or Image to blur the scene after it finishes rendering, which is faster but much less accurate.

We want to select Object, as it is the most accurate method of blurring an object. Click the Object radial button, and then click OK.

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All this does is let the object know that it can now be blurred. In order to finish adjusting our motion blur settings to various degrees, we will have to go into the Render Setup. Press F10 on your keyboard, or find Render Setup in the Rendering menu at the top of your 3D Studio screen. The third button from the right side in the ribbon, the one that looks like a teapot with a little document over top of it will also get you there.

The Render Setup Dialogue will appear. Make sure you have Mental Ray assigned as your Renderer by scrolling to the bottom of the Common tab.

Under the Assign Renderer rollout, click the Top ellipses button and choose NVIDIA mental ray from the list.

Then go back to the top of your Render Setup, and go to the Renderer tab.

This tab houses all kinds of settings specific to the renderer you have chosen in the last step. Filters, Anti-Aliasing, Depth of Field, Camera Shaders, and ... Motion Blur.

Scroll down until you see the Camera Effects Rollout and open it up.

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Turn Motion Blur on by checking the Enable box in the settings rollout.

Uncheck the Blur All Objects button.

This becomes especially important if you are customizing which objects are allowed to blur or not.

If you do want everything in your scene to utilize motion blur, you can leave this checked and then you don't have to turn it on in the Object Properties like we did a few minutes ago. For this demo, we will turn it off.

Mental Ray motion blur has 4 settings which allow you to customize how the blur functions. All we have done so far is turn it on, so let's take a render and see what that does on its own with the default settings. Here is what my propeller box looks like at frame 13 of the animation with Default Motion Blur settings:

Notice that the corners of the box are now blurred.

Next we will adjust the settings in order to refine our blur.

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The first of these settings is the Shutter Duration (frames): settings. Increasing this will blur between more key frames, the larger the number ... the larger the blur and vice versa. Default is 0.5 and gives us just the little bit of blur you saw above.

Let's increase the Shutter Duration to 5.0 instead and take a new render to see the difference.

Quite a difference it is too. Increasing and decreasing this value lets you define exactly how much you wish it to be blurred.

The next setting is the Shutter Offset (frames): This setting defines where motion blur takes an object between frames and begins blurring it. I rarely ever change this at all, usually Default is just fine, so I recommend leaving it alone unless you have a specific reason for changing it.

The next important setting is the Motion Segments: settings. This defaults at 1. Our propeller is moving in a circular rotation but you should notice that motion blur has given it a very boxy straight edge between the frames. By increasing the Motion Segments, motion blur will follow the curve of an object more closely. 1 is fully straight and just blurs directly between the frames and the higher the value goes the more accurate motion blur follows the curvature in the animation.

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I should note that the more you increase this number, the longer the effect will take to render. The maximum is 15 for this value but one rarely needs to go that high. Let's try increasing the value to 5 for now.

Then take another render to see what changed.

Our propeller now blurs along the curve of its rotation like it should. If you go all the way to 15 and render again I doubt you will really be able to see much of a difference, so it is always recommended not to go to the full strength of a setting unless absolutely necessary. Or else you will increase render time for no reason.

The last setting is the Time Samples: settings. This defaults at 5, and is responsible for the cleanliness of the blur. If you notice a high amount of speckled dots in your blur, raising this will smooth it out. It also directly effects render times so choose your value wisely.

Let's try changing it to a Value of 20. and see what happens.

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Take a new render.

Your blur will smooth out a little bit nicer. The maximum value is 100 for this, so in your final render during an animation you can increase this to make our motion blur effect much more even and smooth.

All of these settings work off of the speed an object is traveling, so if you rotate the propeller faster (less frames between key frames) the blur will change with it.

Here is what happens if I speed up my propeller to rotate 180 degrees in only 5 frames instead of 10, and increase my Motion and Time segments for a more polished render.

That is mental ray motion blur in a nut shell! Adjusting these 3 values to your liking can make all the difference in a believable and more realistic animation.

Use it wisely!12