The Associated Press

David G Rutherford

Bernd Helling

David Shaler

David M Shearn

John Kirlick

John H Long

Alain Regnault

Michael S Zarro

Facsimile receiver

A facsimile transmitter capable of transmitting graphic as well as text material, by telephone or wireless. A digital code derived from scanning the document to be transmitted is truncated from eight bits per pixel to six bits per pixel. The three most significant bits of each pixel are run length encoded in eight bit bytes, so that wherever the same three most significant bits appear in adjacent pixels, these three bits are transmitted once, followed by a five bit code indicating the number of times (up to 32 times) the same three most significant bits are repeated in succeeding pixels. The resulting eight bit bytes are similarly run length encoded, so that the transmission of the three most significant bits of each pixel is double run length encoded. An eight bit fine resolution byte is transmitted for each eight pixels. The fine resolution bytes are encoded so that, in conjunction with the double run length encoded three most significant bits of each pixel, (i) the entire six bits of one-fourth of the pixels, (ii) the most significant four bits of one-fourth of the pixels, intermediate between the six-bit pixels, and (iii) only the three most significant bits of one-half of the pixels, each disposed between a six bit pixel and a four bit pixel, are transmitted. At the receiving end the pixels having four bits are expanded to eight bits by averaging the values of the preceding and succeeding pixels for which six bits were transmitted. Then the pixels having three bits are expanded to eight bits by averaging the values of the immediately preceding and immediately following pixels. Each transmitted scanned line contains an error detecting code. When an error is detected in a scanned line at the receiving end, the pixels of that line are replaced by the average of the corresponding pixels of the immediately preceding and succeeding lines.

Method for compression and transmission of video information

A facsimile receiver of the type in which a laser beam modulated by a received video signal scans a light sensitive recording paper to print an image corresponding to the video signal. A feedback loop insures that the output of the laser beam acousto-optical modulator (AOM) accurately tracks the demodulated received video signal. A variable transmissivity filter in the path of the laser beam is automatically positioned to provide increased transmittance as the laser beam intensity decreases with aging of the laser, so as to maintain a constant light output intensity. A lens in the optical system which focuses the laser beam on the paper is moved mechanically as the paper is transversely scanned, so that the focus of the beam is varied to compensate for the planar (non-cylindrical) configuration of the paper, thus keeping the beam focused on the paper throughout the length of each scan line. To minimize bleeding or spreading of the image on the paper, the laser beam output is pulse width modulated inversely with variations in the video signal amplitude, so as to maintain a substantially constant energy per pulse. The amplitude of vertical dither is also varied inversely with the video signal amplitude, to minimize spreading of the scan lines at higher light beam intensity levels. Ripple and patterning in the printed image due to D.C. offset are reduced for video signals transmitted by frequency modulation (FM) or by amplitude modulation (AM), by measuring the duration (for FM) or amplitude (for AM) of each carrier half-cycle and adding a D.C. level to the modulated carrier to minimize the differences in duration or amplitude between successive half-cycles. The demodulated FM video signal is automatically offset and scaled to utilize the entire gray scale dynamic range of the paper on which the image is printed.

Laser printing facsimile receiver

A portable facsimile transmitter suitable for use by reporters and photographers in the field, for sending high quality pictures to an unattended remote receiver, by telephone or wireless. A rotating drum to which the original is affixed is initially scanned at a rapid rate to establish the photodetector operating level so as to maximize the signal dynamic range. After the initial scan the picture is scanned at one of three selectable rates (determined by setting the drum speed), and the video output of the photodetector is modulated and coupled to the transmission line. The original is affixed to the drum by means of a fixed (with respect to the drum) clamp and a movable clamp at each end thereof. A tab extends from an end of each clamp, and the position of each tab is sensed to provide a synchronization signal so that the picture is centered at the remote receiver. A protective circuit begins to measure the drum rotation speed a predetermined time after scanning begins, and terminates transmission if the speed is improper. Picture transmission can be initiated by a command signal from the remote receiver. A reference code identifying the particular transmitter and the place of transmission can be transmitted with each picture.

Portable facsimile transmitter

Growing community of inventors

North Caldwell, NJ, United States of America

David G Rutherford