Cameras are the center of the RenderMan universe. Rendering, baking, map generation - nearly everything you need to do in RenderMan requires a camera to process. Pixar's RenderMan gives artists and TDs advanced control over how CG cameras work, and the two most important aspects of the camera are motion blur and depth of field ... areas where Pixar's RenderMan excels.
In Pixar's Animated short, Presto, one of the challenges was rendering motion blur on the quickly moving characters. RenderMan's innovative blur control, Shutter Timing, was used to help create convincing motion blur.
This subtle effect was critical for creating a specific look, and is an example of the amount of creative control Pixar's RenderMan provides, so any type of creative vision can be realized.
Presto the magician
Blur with an instantaneous shutter
This is the default motion blur from an instantaneous shutter. Look at how even the blur effect is. Sometimes that is the desired look, but in Presto the director wanted blur with more of a stylized falloff, and RenderMan has controls for just that type of effect.
Blur with a slow opening shutter
In this second image, the image was rendered with a slow opening shutter. You'll notice that the blur is shaped ... with the blur looking like it's streaking off the magician. This type of stylized blur was the kind of look the director wanted in this particular case.
In live action film, motion blur is the result of objects moving during the exposure of the film. The faster the exposure, the less things will blur. Conversely, a long exposure results in more motion blur. Audiences are quite familiar with the look of motion blur and creating this effect in 3D fast and efficiently is critical for convincing visual effects.
Pixar's RenderMan can mimic the behavior of real cameras, with extraordinarily fast 3D motion blur. By default, RenderMan renders scenes with an instantaneous shutter speed, an exposure which is impossible in the real world. However, without motion blur the effect would look unnatural, as moving objects would strobe across the screen, causing temporal aliasing.
Thankfully RenderMan is extremely efficient at rendering motion blur and has a number of options to help tune the final look.
There are many knobs for controlling the quality and character of motion blur. Here are some of the most important.
In the real world, when a camera focuses on a close object, the background can go blurry. This effect is known as the depth of field, and Pixar's RenderMan offers many controls for creating this effect.
With Pixar's RenderMan, we can decide, depending on requirements, whether we want finite or infinite depth of field, an instantaneous shutter speed or a long one to create motion blur. RenderMan provides us with several options to control how our virtual camera behaves, which is important for creating believable 3D imagery.
Depth of Field in RenderMan is dependent on three main factors: the focal length of the lens, the diameter of the aperture, and the focal distance of the camera. With these controls RenderMan can convincingly emulate real film cameras.
TM & © 1986 - Pixar. All Rights Reserved.