Motion Blur

 

These settings control the amount, type, and quality of motion blur. Arnold can apply motion blur to cameras, objects, lights, and shaders.

Increasing the number of Camera (AA) samples is the only way to decrease motion blur noise.

To generate motion vectors, set an instantaneous shutter on the camera.

Enable

Enables motion blur.

Deformation

This option specifies whether motion blur will take into account geometry deformation. This should only be enabled when objects in the scene change shape quickly enough since this option uses more memory and renders slower. Adding motion blur to hair also requires Deformation Keys.


Deforming objects such as hair or grass require deformation motion blur


Camera

Switch for enabling/disabling camera motion blur.

Keys

The number of sub-steps used for motion blur can be set in the keys attribute within the Motion Blur settings. For situations where there is a direct movement, such as translation and rotation with constant speed, two keys are enough. However, if the object moves erratically during the exposure interval or performs any other kind of non-linear movement, you will need to increase the number of keys. 

Increasing the number of keys does not usually have much effect on rendering times, although it requires more memory to store the additional geometry at multiple times, especially for large polygon meshes. 

Below are examples where an increase in the number of keys is required. Notice that increasing the number of keys rounds off the corners of the spinning wheel:

 

The effect is more apparent when animating a deforming object along a motion path:

Keys 2 (rollover image).

Keys 4 (rollover image).

Keys 8 (rollover image).

Shutter Controls

Position

Specifies an Offset for the shutter’s time interval which allows you to change the motion blur trails. The Position offsets the motion blur within the image. It is a relative value that extends towards the frame. 

This setting allows you to control when the camera shutter opens and closes relative to the frame being rendered. 

Start on Frame

The shutter opens at the current frame. For example, rendering frame 5 with a length of 1 would result in the times 5.0, 5.5, 6.0 being calculated.

Center on Frame

The shutter is open during the current frame. For example, rendering frame 5 with a length of 1 would result in the times 4.5, 5.0, 5.5 being calculated. 

End on Frame

 Makes the shutter close at the current frame. For example, rendering frame 5 with a length of 1 would result in the times 4.0, 4.5, 5.0 being calculated. 

Custom

Allows you to define the start and end point for the motion range.

Custom Shutter Angles rendered at frame 0

Length

 

You can use this attribute to tweak the size and length of the motion blur trails. Normally this won't be bigger than one frame unless you are looking for an exaggerated effect.

  • When set to 0, neither geometry nor camera motions are considered.
  • Smaller values create a subtler motion blur effect.
  • Larger values create a wider or longer motion blur effect, simulating a faster speed.

To get an 180 degrees shutter angle, you should use a length of 0.5 frames (since the exposure time will be 1/48s (assuming you are using 24 fps), which is the equivalent to 0.5 frames).
To get 360 degrees, you should use a length of 1 and to get 90 degrees you would, therefore, use a value of 0.25.

A value of 0 yields no motion blur, while larger values create longer blurred trails, simulating a faster speed. The standard value is 0.5, equivalent to an 180° shutter angle.

The shutter length is equivalent to the exposure time above.

  • 45° shutter angle = Shutter length 0.125
  • 90° shutter angle = Shutter length 0.25
  • 180° shutter angle = Shutter length 0.5
  • 360° shutter angle = Shutter length 1

 

Example render using a long shutter length

Ignore motion blur. This can be useful for debugging problematic scenes with motion blur. When ignore motion blur is enabled, Arnold will use the geometry state defined by the reference_time parameter (located in the options node as well and in the range of 0-1).


Ignore Motion Blur can be found under the list of Feature Overrides in the Diagnostics tab.

Motion Blur Noise

Very long key ranges will produce exaggerated motion blur, but will also cause more noise to appear within the motion blur trail. Increasing the number of Camera (AA) samples will reduce this noise (see example below).  

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