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Digital erase of raster lines

  • US 4,360,805 A
  • Filed: 10/01/1980
  • Issued: 11/23/1982
  • Est. Priority Date: 10/01/1980
  • Status: Expired due to Term
First Claim
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1. A method of obscuring the perception of a base raster of a raster scan display device by bidirectionally vertically shifting said base raster in a manner in which a sequence of other rasters are produced with a maximum shift of any one of such other rasters in either direction being less than the distance between a pair of adjacent horizontal scan lines of said base raster, said base raster being produced by scanning an electron beam in response to original vertical and horizontal sync pulses, said method comprising:

  • presenting a predetermined number of rasters with the horizontal lines thereof shifted vertically by a predeterminedly-changed amount in a cyclical sequence wherein(a) in one stage of said sequence, rasters are presented each at an increasingly higher position relative to the position corresponding to said base raster in response to(i) delayed vertical sync signals each of which is predeterminedly increasingly delayed relative to the corresponding original vertical sync pulses, and to(ii) original horizontal sync pulses, and(b) in an opposite stage of said sequence, rasters are presented each at a lower position relative to the immediately preceding raster in response to(i) delayed vertical sync signals each of which is delayed by a predeterminedly decreased amount of time relative to the time of delay of the immediately preceding delayed vertical sync signal, and to(ii) original horizontal sync pulses.

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