Apple MA434Z/A User Manual - Page 876

seed The random seed for the grain. When Shake generates a random pattern of values, you need to make sure for purposes of compositing that you can recreate the same random pattern a second time. In other words, you want to be able to create different random patterns, evaluating each one until you find the one that works best, but then you don't want that particular random pattern to change again. Shake uses the seed value as the basis for generating a random value. Using the same seed value results in the same random value being generated, so that your image doesn't change every time you re-render. Use a single value for a static result, or use the expression "time" to create a pattern of random values that changes over time. For more information on using random numbers in expressions, see "Reference Tables for Functions, Variables, and Expressions" on page 941. filmResponse The valid range is theoretically infinite, but practically is -1 and 1. -1 is typical of standard film, with grain applied to the entire range except the brightest whites, and black is the most affected. 1 is the inverse of that, withholding grain from the darks, with most grain on the whites. Default is -1. lGain, rGain, gGain, bGain The overall intensity of the grain. lGain (luminance) applies to all three channels equally, while rGain, gGain, and bGain apply only to each particular color channel. Each of these parameters has subparameters for adjusting its bias, LowOffset, and HighOffset values. • bias: Shifts the grain level higher or lower in intensity. • LowOffset: From the midpoint of the Gain, squeezes the darker grain areas. This is a useful adjustment when the highlights are good and you want to modify only the level of the darker grain. • HighOffset: From the midpoint of the Gain, squeezes the brighter grain areas. aspect The grain aspect ratio. An aspect of 2 stretches it twice as wide. softness A value above 0 softens the grain. A value below 0 sharpens the grain. The global softness is an additive factor, so it is added to the values of the per-channel parameters. obeyAlpha When enabled, grain is applied to the image through its alpha channel. When disabled, grain is applied to the entire image, and the alpha is ignored. Useful for applying grain to premultiplied CG images without contaminating the background black. 876 Chapter 28 Filters