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Method and apparatus for producing grey levels on a raster scan video display device

  • US 5,400,044 A
  • Filed: 12/16/1993
  • Issued: 03/21/1995
  • Est. Priority Date: 06/29/1990
  • Status: Expired due to Term
First Claim
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1. Apparatus for driving a one-bit-pixel raster scan video display device, having a display which comprises a plurality of rows each consisting of a plurality of pixels, to display a plurality of grey levels, which apparatus comprisesmeans for generating an input signal for the display device to illuminate selected pixels thereby to indicate the desired grey level, the said means including:

  • means for generating a plurality of repetitive grey level signals, each having a respective repeat period equal to n number of bits wherein n is not the same number for each grey level, each grey level signal being indicative of a selected proportion of pixels to be illuminated to display the corresponding grey level;

    selector means for selectively applying a said grey level signal as the input signal to the display device in dependence upon the desired grey level of the region of the display addressed; and

    signal adjustment means, adapted to introduce a row phase shift in each grey level signal, in response to an indication that a new row is to be addressed by the input signal, to cause illumination in successive rows of each frame of a different corresponding plurality of pixels for the same desired grey level, and adapted to introduce a variable frame phase shift of f bits into each grey level signal, in response to an indication that a new frame is to be addressed, to cause illumination in successive frames of a different corresponding plurality of pixels for the same desired grey level,wherein, when the repeat period equal to n for the respective grey level is odd, the frame phase shift f is co-prime and is as close as possible to n/2, andwhen the repeat period equal to n for the respective grey level is even, the frame phase shift f alternates between (n+2)/2 and n/2, or between n/2 and (n-2)/2).

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