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Motion Blur
RenderMan has a number of controls for creating fast and efficient motion blur.

Motion Blur: Enabling motion blur causes moving objects to be blurred along their path of movement in order to prevent temporal aliasing and strobing. When using motion blur, you should increase the number of pixel samples (in the Quality subpanel), and expect longer rendering times.

Motion Factor: A special geometric approximation type, Motion Factor provides a processing/quality tradeoff for motion blurred objects — because the objects are blurred, less detail is required and a higher shading rate will be sufficient. A Motion Factor value of 0.0 will turn this feature off. Values greater than 1.0 will cause motion blurred objects to have their effective shading rate raised (the default value is 3).

Camera Blur: The renderer will ignore the movement of the camera when computing motion blur when this feature is disabled. If you do move the camera and want everything in the scene to blur accordingly, you will need to turn this feature on; however, you should expect this to be a potentially expensive operation since everything in the scene will now undergo motion blurring calculations.

Shutter Angle: This setting is only meaningful when Motion Blur is enabled. It controls how long the shutter is open during a frame. Measured in degrees a setting of 360 opens the shutter for the entire frame. The larger the angle, the greater the blur, which increases render times. 

Shutter Timing: This field allows you to control when the virtual camera shutter opens, and is only meaningful when Motion Blur is enabled. The default value Open on Frame causes the shutter to be open from frame to frame + shutter angle. If you choose Center on Frame, the shutter will be open from frame - shutter angle/2 to frame + shutter angle/2. Note that, in RenderMan, shading calculations occur only at frame open time, and thus shadows and reflection maps will be computed only at shutter open time.

Motion Blur Type: The Frame option causes the positions of all objects to be calculated only at frame boundary times, and will rely on the renderer to perform linear interpolation of the object positions in order to determine where they are at shutter open and close times. The Frame option results in faster rendering, at the expense of less accurate motion blur. Enabling subframe motion will cause the position of objects to be calculated exactly at shutter open and close time, creating blur with higher fidelity, at a slightly increased cost.

Ray-Traced Motion Blur: Controls whether motion blurred objects appear in ray traced results. If your reflective object is moving or deforming you should disable this parameter to avoid self-intersection artifacts. If your mirror isn't moving, set this to 1 to see the reflected objects properly blurred. 

Ray Tracing
Ray tracing provides a system for creating a variety of effects, from reflections and refractions to fancy global illumination effects like occlusion and color bleeding. Occlusion determines the amount a point is obscured by other surfaces, creating subtle shadows. Color bleeding is similar to occlusion but “bleeds” color from other materials. Occlusion and color bleeding data are calculated by casting many hemispherical samples from a given surface point.

Ray Tracing: Control for enabling/disabling ray tracing. Ray tracing effects can be expensive, so ray tracing can be turned off to enable faster scanline rendering. 

Trace Bias: This value is added to the ray origin when tracing rays to overcome numerical precision issues resulting in false ray-primitive intersections. This value acts as the scene default and you can override this value on a per-primitive basis via RenderMan Attributes. 

Max Ray Depth: This sets a limit to the number of bounces any ray can travel regardless of its type.

Max Specular Depth: Limits the number of specular bounces (reflections and refractions) for rays traced from the associated primitive. A value of 1 or 2 is a reasonable default unless you need multi-bounce effects. This value acts as the scene default and you can override this value on a per-primitive basis. 

Max Diffuse Depth: Limits the number of bounces (diffuse or specular) for indirect illuminance relative to the associated primitive. You can use this attribute to limit the number of diffuse and specular bounces of photons in the photon tracing pass as well as to limit the depth of diffuse illuminance gathering shaders. A value of 1 is suggested. This value acts as the scene default and you can override this value on a per-primitive basis via RenderMan Attributes.

Global Illumination
Global illumination effects, such as occlusion, color bleeding, and Image-Based Illumination (IBI) can be created using the RenderMan Environment Light. Clicking on the checkered box creates a new node and displays the controls for the RenderManEnvLight in the Attribute Editor. Ray tracing must be enabled to create an Environment Light. For more information on global illumination, see the Global Illumination Tutorial.


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