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Automatic shift circuit for a sub-picture screen for picture-in-picture feature

  • US 4,998,171 A
  • Filed: 08/28/1989
  • Issued: 03/05/1991
  • Est. Priority Date: 07/05/1988
  • Status: Expired due to Term
First Claim
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1. An automatic-shift circuit for a sub-picture screen for a Picture-In-Picture feature, comprising:

  • brightness signal separation means for separating a brightness signal from a composite video signal for a main picture screen;

    brightness level comparison means connected to said brightness signal separation means, for detecting character brightness level and width from the repeated brightness signals to detect the presence of characters from said separated brightness signal;

    identical position comparison means connected to said brightness level comparison means for comparing a previously detected brightness width with a next detected brightness width in order to generate a SET signal if the next detected brightness width occupies the same position as the previously detected brightness width, or a RESET signal if the next detected brightness width occupies a position different from the previously detected brightness width;

    timing setting means for setting vertical and horizontal timings of the sub-picture screen from vertical and horizontal sync signals of the main picture screen, and setting vertical and horizontal timings of character area based on the SET and RESET signals of said identical position comparison means;

    counting means for counting a number of fields having the vertical and horizontal timings of the character area of said timing setting means set, and for generating an automatic-shift signal when the count exceeds a prescribed value; and

    a microcomputer for generating control signals from said automatic-shift signal, and for shifting the primary specified position of the sub-picture screen within the main picture screen to a prescribed secondary or tertiary position.

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