Controlling Motion Blur in Renderman

Enabling motion blur in RenderMan results in objects to be blurry when they are in motion. This results in the objects looking more interesting and realistic. The pixel numbers need to be increased, and longer rendering times should be expected. There are a number of controls that need to be used for creating a motion blur. The motion blur is under the features tab in the render settings.

Step 1: Motion Factor

The motion factor gives a tradeoff for the objects that are blurred. This is justifiable because very little detail is needed, and therefore the shading rate should be higher. If you put the motion factor value at 0.0, the feature will be turned off. If you put it at a value that is greater than 0.1, objects that are motion blurred will have their rates of shading raised.

Step2: Camera Blur

This feature should not be active when the renderer is working on the motion blur. For a blurry effect for everything in the scene, then the feature will need to be turned on. This operation, however, is expensive since a lot of motion blurring calculation is involved.

Step 3: Shutter Angle

This feature is only applicable when the Motion Blur is active. This setting determines the duration that the shutter should be open during a frame. A 360 degree setting will enable the shutter to open for the whole frame. The bigger the angle, then the larger the blur, which eventually increases the render times.

Step 4: Shutter Timing

This feature helps in the control of the virtual camera once the shutter is open. It is only applicable when the Motion Blur feature is enabled. The value Open on Frame results in the shutter opening from frame to frame plus the shutter angle. If you happen to select Center on Frame, then the shutter will open from frame to shutter angle/2 to frame plus shutter angle/2. It is important to note the calculations are only done during the frame open time, which means that the reflection maps and shadows will be calculated only during shutter open time.

Step 5: Motion Blur Type

This Frame option results in all object positions being calculated at only frame boundary times. It only relies on the renderer to work on linear interpolation of the position of the objects so that it can know their positions at shutter open as well as close times. The Frame option makes rendering faster, which has an effect on the motion blur. When the sub-frame motion is enabled, the object positions will be computed immediately from shutter open and close time, which will result in a blur being created with a fidelity that is higher at a cost that is increased.

Instantaneous Shutter Speed works in RenderMan by default. This, however, in the real world is impossible. The effect, however, needs motion blur for it to look natural. The Ray-Traced Motion Blur controls the way the objects that have motion blur appear in the ray traced results.