Adobe 65008009 - After Effects CS4 Using Manual page 530

Last updated 12/21/2009
Working with added or matched grain
The Add Grain effect creates new grain or noise in an image by building the grain from nothing or by basing the
properties of the grain on presets. The Match Grain effect also creates new grain in an image but by matching the grain
in a different image. Both effects share several controls in the Effect Controls panel that let you control the color, tonal
range, blending mode, and animation properties of the grain.
Adjusting the tones of added or matched grain
The precise grain pattern present in any frame of film isn't uniform throughout the frame but may depend on the tonal
values of the content at each pixel. For example, in chemical film grain, the sizes of the silver halide crystals vary with
the exposure level.
The Add Grain and Match Grain effects let you reproduce these subtle changes in grain patterns across areas of an
image or a sequence by using the Shadows, Midtones, Highlights, and Midpoint controls in the Application controls
group. These controls let you define how much grain is added to each tonal area and also to each channel in the image.
For example, you can add more grain to overexposed areas of the blue channel to give an image of sky a grainier look.
You can use the Application controls group for the Add Grain or Match Grain effect to do the following:
• To define how much grain is added to each tonal area in an image, adjust the Shadows, Midtones, and Highlights
values.
• To define the midpoint of the tonal range of the image for grain application purposes, adjust the Midpoint slider.
By default, this slider is centered at 0.5, which represents the middle of the range of pixel values—127 for 8-bpc
images and 16384 for 16-bpc images.
• For even finer control, use the Channel Balance controls to adjust the grain in the shadow, midtone, and highlight
areas independently for each channel.
Animating added or matched grain
By default, the grain or noise generated by the Add Grain and Match Grain effects moves at the same speed as the
source material to accurately simulate realistic noise. Slowing down the noise processes may be useful for aesthetic
effect or to keep the added noise from buzzing and drawing attention to itself. These effects have an internal
randomizer that changes the positions of the noise pixels between frames. But you can also change the appearance of
the noise between layers on the same frame while keeping every other parameter constant.
You can use the Animation controls group for the Add Grain or Match Grain effect to do the following:
• To specify the frame rate of the added grain, as a multiple of the destination frame rate, adjust the Animation Speed
value in the Animation controls group in the Effect Controls panel. At higher Animation Speed values, the lifespan
of the grains is lower. At the default value of 1, the grain moves at the same rate as the frames. At lower values, the
grain changes more slowly, which can be useful for giving the appearance of film grain. At zero, the grain is
stationary over time.
• To use interpolation to create smooth transitions between the generated noise frames, select Animate Smoothly.
This control matters only if Animation Speed is less than 1.
• To change the appearance of the noise between layers on the same frame, adjust the Random Seed value. Each
Random Seed value represents one of 100 possible variations in the appearance; changing the value doesn't make
the results more or less random.
Blending and adjusting the color of added or matched grain
You can adjust the color, saturation, and blending behavior of the grain generated by the Add Grain or Match Grain
effect.
USING AFTER EFFECTS CS4
Effects and animation presets
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