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The number of substeps used for movement blur can be set in the global render options. For simple movement, such as translation and rotation with constant speed, two steps are enough to reconstruct the correct motion. However, if the object accelerates or changes direction during the exposure interval or performs any other kind of non-linear movement, you will need to increase the number of steps until a reasonable look is achieved. The following images illustrate an extreme case where an object moves along a complex path while the shutter is open:
Path in the Maya viewport, for reference. |
With 2 steps, the object follows a straight line |
10 steps are still far from enough to capture |
100 steps are needed to come close to the |
Increasing the number of steps does not usually have a large impact on the rendering performance, but can slow down the export process if the scene has complex relationships which take long to evaluate when the current time is changed.
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This setting allows you to control when the camera shutter opens and closes relative to the frame being rendered. When set to 0, the shutter opens at the start of the frame, so the future movement is captured, while a value of 1 makes the shutter close at the start of the frame, so only the past movement is seen. A value of 0.5 centers the exposure interval on the current frame. The following images demonstrate the effect of this parameter in a scene where a emitter sphere moves from left to right over the duration of 3 frames. The shutter angle is set to 360 degrees, so the exposure interval is equal to one frame:
Screenshot showing the position of the sphere |
Rendering frame 2 with offset 0. Only movement |
Changing the offset to 0.5 captures movement |
Offset 1 ends the exposure on the current frame, |
Skinning and Binding
Movement which results from skinning can only be exported as deformation, even if rigid binding is used. In Maya terms, movement blur is only computed based on changes to the attributes of the transform nodes. Anything which is inserted in the construction history of the shape - deformers, tweaks, joint clusters, skin clusters etc. - is seen as deformation by the plug-in.
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The position of the end joint in frames 1 and 2. | |
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Rigid bind. |
Parented to end joint. |
When skinning is used, the movement is exported as deformation. If you set the blur type to Movement Only, no motion blur is rendered. You can notice how the trajectory of the left end of the object is incorrect - it's linear instead of following a curved path, as if the object is shrinking and then enlarging during the motion. In contrast, when the object is parented to the joint, the correct rotation is rendered and Maxwell uses the more efficient movement blur method.
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See the Exposure section in the camera documentation for details on how you can control the shutter interval without affecting the image exposure. Most of the time when working with animation, you will probably find it easiest to use the camera in rotary shutter mode.