Bell Telephone Laboratories

Edward George Bowen

Arun N Netravali

Frank W Mounts

A pseudo-gray scale signal obtained by comparing the intensity values of elements of a picture with a series of spatially dependent threshold values is processed for display on a multilevel device. Generally, an estimate of the intensity value of each pel is formed as a joint function of the display words which make up the pseudo-gray scale signal and an indication of the threshold value associated with the pel. In one embodiment, the display words and threshold values are used to select appropriate stored intensity values obtained from representative pictures. Alternatively, the estimates are derived recursively using display words and threshold values for a neighborhood near the pel being processed.

Display of pseudo-gray scale picture signals on multilevel displays

A facsimile scene typically includes a plurality of lines, each line having a plurality of picture elements (pels). Often, pel signals are adaptable for run-length coding, a run being one or more successive pels having the same brightness level. To increase the length of a run and hence to permit a more efficient use of a transmission link, a processor is disclosed for permuting a measure of the pel signals responsive to a reference signal. Illustratively, the reference signal is the pel signal from a previous line. In one exemplary bi-level pel signal embodiment, the measure is the current pel signal. Specifically, if the reference pel signal is a logic one, the current pel signal is loaded beginning at one end of a memory; if the reference pel signal is a logic zero, the current pel signal is loaded beginning at the other end of the memory. In a second embodiment, the measure is an error signal for indicating a difference between the reference signal and the current pel signal. But for loading the error signal rather than the current pel signal, the operations aforedescribed are again followed.

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Lawrence Harbor, NJ, United States of America

Edward George Bowen