Staggered scan facsimile

摘要

1,127,048. Television; copying by scanning. XEROX CORP. 3 Jan., 1966 [4 Jan., 1965], No. 203/66. Heading H4F. To improve the image quality in a time and amplitude quantized facsimile or television system the transitions in different lines of transmitted video is synchronized to different clock signals having a common frequency but different phase, so that when reproduced the signals create marks which no longer line up in vertical rows i.e. the black-white transitions are staggered or offset from line to line. The video signal may be amplitude quantized in two steps, e.g. black and white, or more than two steps, and although preferably the transitions in alternate lines are offset by half the normal spacing between transitions the staggering may be such that only every third line is vertically aligned or the transitions in individual lines may be positioned in a random fashion. Since a staggered signal which changes in phase from line to line is not suitable for transmission over most communication links the signal before transmission is preferably passed through a variable delay circuit wherein the phase of the signals is altered to bring them into synchronism. Instead of synchronizing the sweeps of the transmitter and receiver to the clock reference and altering the phase of the signal derived from or supplied thereto as described in the detailed embodiment, the stagger may be introduced by altering the phase of the scanner or recorder sweeps with respect to the clock reference or by stepwise operation of a scanner.