A technique for representing the entire gray scale of a picture by picture elements with only one of two levels (``white'' and ``black''), in which a multilevel input image signal is compared with a position- dependent set of thresholds, and picture elements are set to ``white'' only where the image input signal exceeds the threshold.

A force having a controlled amplitude and frequency, applied continuously to a device driven by a servomotor so that the device is constantly in small-amplitude motion and cannot stick at its null position. Also known as buzz.