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About layer maps (PB only)


    A layer map is an image in which each pixel's brightness value is used by an effect in a calculation. Particle Playground uses a layer map to exercise precise control of a particle property such as opacity. In this way, After Effects doesn't use a layer map as a picture but as a matrix of numbers. In many cases, you never see the actual layer map in the final movie--you only see the result of an effect applying the layer map's pixel values to the corresponding pixels in a destination layer.

    Layer maps (left) can change properties of the particles that pass over them, such as scale (right).
    Layer maps (left) can change properties of the particles that pass over them, such as scale (right).

    Regardless of the color depth of the image that you use as a layer map, After Effects always uses its red, green, and blue channels as if each were an 8-bit grayscale image. If you create a layer map using colors, the Property Mappers in Particle Playground can extract the brightness values from each RGB color channel separately (see Using layer-map RGB channels to alter multiple properties independently (PB only)).

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