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Motion Blur#

By default, motion blur is disabled. To enable motion blur you must activate it by setting Motion Blur Mode to 3D Motion Blur.

The quality of the motion blur is controlled using Anti Aliasing Sample Count. Please note that the raytracer provides several motion blur modes:

Mode Description
Disabled Motion blur is disabled.
Motion Vectors Only motion vectors are computed and the image is not blurred. The time at which motion vectors are computed can be controlled with the Shutter Begin attribute.
3D Motion Blur The motion blur is computed but the motion vectors are not computed.
3D Motion Blur + Motion Vectors Motion blur and motion vectors are computed.

When enabling motion vectors, an extra vector is computed and stored in shaded fragments. It is possible to access to the value of this vector either by enabling the corresponding motion_vector AOV using the AOV Editor or by using the Utility texture node. The following images show the result of the different modes and display motion vectors values.

Motion blur disabled

Motion vectors enabled

3D motion blur enabled

3D motion blur and motion vectors enabled

Important

Motion Vector AOV is a normalized vector in image space so that the vectors are resolution independent. To get the actual extent in pixel, you must multiply the vector by the width and height of the image.

Motion Blur Settings#

The raytracer supports several types of motion blur: Backward, Centered, Forward. It is also possible to define the number of time samples as well as the time range that must be sampled.

These settings are also accessible in the Rendering tab of Project Preferences (Edit > Preferences...) and on the raytracer itself.

Backward motion blur

Centered motion blur

Forward motion blur

Attribute Description
Motion Blur Settings Select if the settings that must be used are the ones from the project preferences are the ones defined by the raytracer.
Motion Blur Sample Count Define the number of time samples. A high number of samples is better for non linear motion but it requires more memory.
Motion Blur Direction Define the direction of the blur (Backward, Centered, Forward).
Motion Blur Length Define the length of the time range that must be sampled. A value of 100% corresponds to the entire duration of the frame.

Shutter Range#

When computing motion blur, the raytracer needs to sample the time and compute the position of objects at each time sample. These positions are then interpolated when evaluating time between time samples. The time of these samples depends only on the Motion Blur Settings that are found in the global preferences (Sample Count, Direction and Length). Shutter Begin and Shutter End attributes allow to set the range of the frame that needs to be computed. They doesn't affect the time of the samples.

*A rotating object with 4 motion samples and a shutter range of [0.0, 1.0]

A rotating object with 4 motion samples and a shutter range of 00, 10

The same object with a shutter range of [0.2, 0.6]. We can see that the time of the samples is the same.

The same object with a shutter range of 02, 06 We can see that the time of the samples is the same

Shutter Curve#

By default, samples are exposed for the same amount of time. The Shutter Curve basically simulates how fast/slow the shutter opens between each frame. It can be used to finely control the aspect of the motion blur and match live action for example. This attribute can't be used to simulate rolling shutter.

constant shutter curve

triangle shutter curve