Noise & grain effects, Work with grain effects – Adobe After Effects CS3 User Manual
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AFTER EFFECTS CS3
User Guide
452
Noise & Grain effects
Work with Grain effects
Almost every digital image captured from the real world contains grain or visual noise caused by the recording,
encoding, scanning, or reproduction processes and by the equipment used to create the image. Examples include the
faint static of analog video, compression artifacts from digital cameras, halftone patterns from scanned prints, CCD
noise from digital image sensors, and the characteristic speckle pattern of chemical photography, known as film
grain.
Noise isn’t necessarily bad; it’s often added to images to create a mood or tie elements together, such as adding film
grain to a computer-generated object to integrate it into a photographed scene. However, noise can be unwanted for
aesthetic reasons. Archival footage or high-speed photography may appear unpleasantly grainy; digital compression
artifacts or halftone patterns may mar an image; or noise may interfere with technical processes such as bluescreen
compositing.
There are also technical reasons to reduce noise. For example, compression algorithms usually achieve smaller file
sizes if the input material is less noisy, so noise reduction is a valuable preprocessing step for work such as DVD
creation and video streaming.
The Add Grain, Match Grain, and Remove Grain effects allow you to manipulate grain that appears more or less
evenly over an entire image. Grain effects can’t correct image problems that affect only a few pixels, such as dust, salt
and pepper noise, or analog video dropouts.
The Add Grain effect generates new grain from nothing; it doesn’t take samples from existing grain. Instead, a
number of parameters and presets for different types of film can be used to synthesize different types of grain.
The Remove Grain and Match Grain effects use a two-step process to manipulate grain without affecting the edges,
sharpness, or highlights of an image. First, the grain is sampled, either automatically or manually; second, the grain
is analyzed and portrayed by a mathematical model, which the effect uses to add, remove, or match the grain.
Three types of grain effects: matching (top left), adding (bottom left), and removing (bottom right)
RE:Vision Effects provides the DE:Noise plug-in for removing noise and grain from images:
.
Neat Video provides the Reduce Noise plug-in for removing noise from digital video: