These settings control the amount, type and quality of motion blur. Arnold can apply motion blur to cameras, objects and lights. All together, these settings define the times at which the scene is evaluated to collect the points, normals, etc. that are then processed when tracing the scene. Extra camera-specific motion blur settings can be tuned in the motion blur tab of the camera options property.
Increasing the number of Camera (AA) samples is the only way to decrease motion blur noise.
The number of motion keys for matrix transformation. Transformation motion blur is calculated based on a linear interpolation of an object transform matrix, between successive motion keys. Increasing this value will add extra steps, which can improve the blurred result. The default is 2, which results in straight lines of blur between shutter start and shutter end. For situations where there is a direct movement, such as translation and rotation with constant speed, two steps 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 Transformation Keys does not usually have much effect on rendering times, however you may notice a small increase.
The effect is more apparent when animating a deforming object along a motion path:
Transformation Keys 2 (rollover image).
Transformation Keys 4 (rollover image).
Transformation Keys 8 (rollover image).
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.
Here you can enable deformation motion blur, and set the number of Keys for it. Deformation blur takes into account geometry deformation, and should only be enabled when objects in the scene change shape quickly enough, since this option uses more memory and renders slower.
This option applies to pointclouds. By default, pointclouds are blurred according to the PointVelocity attribute, or to the StrandVelocity attribute (for strands). Such attributes define the velocity at the current fame, and are not sub-sampled by the ICE module. As a result, motion blur on poinclouds is pretty fast to compute, but linear.
For a more detailed result, with this flag you can tell the exporter to sample the pointcloud at the actual motion blur times, thus ignoring the velocity attributes. However, this requires caching the simulation to disk. See ICE Motion Blur for details.
Define when and how the camera shutter opens and closes. The amount of blur is proportional to the time that the shutter remains open (i.e. shutter length or shutter end minus shutter start).
Controls when the camera shutter opens and closes relative to the frame being rendered. Options are Start on Frame, Center on Frame, End of Frame, Custom.
If Position is Start on Frame, Center on Frame, or End of Frame, defines the length, in frames, of the motion blur trails. Normally this won't be bigger than 1 frame unless you are looking for an exaggerated effect. 0 means no motion blur.
Example render using a long shutter length
If Position is Custom, these are the start and end time, within the current frame, where the camera shutter opens and closes.
Custom Shutter Angles rendered at frame 0
Values higher than 1 produce intense motion blur, but may also cause artifacts to appear in the rendered image. Increasing the number of AA Samples will reduce noise within the motion blur trail (see example below).