Adjusting Aperture Controls in Renderman

RenderMan is an application program interface that controls how both the modeling software and animation software communicate to the rendering software. It is actually the communication protocol. In order to have a complete image, the interface is essential in addition to shaders and renderers. You can add aperture controls to your camera by using the attribute editor. These controls will allow you to manipulate the shapes of your lens and other characteristics, simulating the features of an actual camera’s lens. While adjusting the aperture in RenderMan, there are a few parameters to consider.

The Side Parameter

This is the number of sides of the aperture. If the shape of a circle is blurred, the number of available diaphragm blades will control this. If for instance the backward compatibility is less than a preferred value, then this will be reverted to its previous behavior by using a circular aperture.

The Angle Parameter

This is in degrees, and from a reference direction, you realize the polygon’s orientation. A vertex on the X axis is put by the 0 degrees. This angle parameter is useful in rotating points that are out of focus.

The Density Parameter

Sometimes density is also known as brightness. Density is supposed to be constant and the parameter helps in controlling the slope of brightness. When this parameter is zero, the density is also constant. When it is towards negative after zero, the aperture becomes brighter near its center. There is a range of legal values for the brightness which is -1 to 1. This control is very important in defining the light that is needed.

The Roundness Parameter

This is nothing but a shape parameter. It also has legal values that range from 1 to -1. When 0, the aperture takes a regular polygon’s shape with straight sides. If it gets to 1, it is actually a real circle. Between the 0-1 ranges, you will realize polygons which have edges that are curved and bowed out. The polygons edges will bow in when the value is negative. In general, the roundness parameter will control the curves realized from aperture blade’s edges.

To play with your focus effects on Pixar’s RenderMan, you will browse to attributes then RenderMan, followed by aperture controls. Here, you will be able to use all of the above features to your comfort. You can try to set up a picture to be sharper. Sometimes to renderman with motion blur, you will look at the play animation and see some of the motion on character, and can actually stop on frame and render to have a look. You also have a choice of pixels to play around with to your satisfaction for better quality.

There are 3 common settings for exposure control, namely:

  1. Shutter priority - uses shutter speed, and  can adjust the F-stop
  2. Aperture priority – uses the F-stop to adjust shutter speed
  3. Programmed - Adjusts both the shutter speed and F-stop

The Lens aperture also known as Bokeh controls the shape of the lens for special depth effects.