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Non-linear contrast control apparatus with pixel distribution measurement for video display system

  • US 5,422,680 A
  • Filed: 08/24/1994
  • Issued: 06/06/1995
  • Est. Priority Date: 05/22/1992
  • Status: Expired due to Term
First Claim
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1. A video signal processing system for use in a given apparatus, comprising:

  • first means responsive to a given one of a video input signal and a video output signal of said system supplied thereto for generating a count representative of the total number of picture elements that occur within a given time interval of at least one field interval of said given video signal and which have video signal levels that lie within a predetermined range of values with respect to a given video reference level;

    second means for comparing the count of said first means with a given percentage of the total number of the picture elements occurring within said given time interval for generating a control signal;

    controllable means, having a controllable transmission characteristic and having a control input to which said control signal is applied for altering the transmission characteristic of said video input signal supplied to said controllable means in a sense to said form a video output signal representative of images having selected response characteristics controlled as a given function of said count; and

    wherein;

    said given apparatus comprises a television picture reproducing apparatus;

    said use in said apparatus comprises contrast modification of the images produced by said apparatus;

    said contrast modification is non-linear for altering the contrast of areas of one brightness level of said images differently than areas of another brightness level;

    said predetermined range of values comprises values equal to or less than said given video reference level;

    said controllable means comprises a non-linear transfer function generator having an input coupled for receiving said video input signal;

    said given video signal applied to said first means is taken from said video output signal produced by said non-linear transfer function generator for causing said video signal processing system to be subjected to feedback control of the contrast of said video output signal so as to provide a predetermined percentage of black pixels in displayed images.

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