Mask

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In Adobe Photoshop and similar image-editing applications, a mask is a greyscale image that acts like a physical mask used for airbrushing, where the presence of the mask prevents a change to the layer.

In Photoshop, masks are generally associated with layers, and can be used to prevent part of a layer appearing, or to prevent an effect being applied across part of the image. White allows the effect or layer to be fully visible, black prevents its action, and grey levels allow a certain proportion through.

Skilful use of masking turns any plugin or filter into an adaptive effect.