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Infrared imaging system having an automatic focusing control

  • US 5,404,013 A
  • Filed: 09/10/1993
  • Issued: 04/04/1995
  • Est. Priority Date: 02/25/1993
  • Status: Expired due to Fees
First Claim
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1. An infrared imaging system comprising:

  • a lens system for focusing a two-dimensional infrared image of an object on an image plane of said lens system;

    a lens drive mechanism carrying said lens system such that said lens system is movable along an optical axis of said lens system;

    an infrared detection array comprising a plurality of infrared detection elements arranged on a plane, for producing output signals indicative of said two-dimensional image of said object;

    display means supplied with said output signals from said infrared detection array for displaying an image of said object;

    filtering means supplied with said output signals from said infrared detection array for extracting high spatial frequency components therefrom;

    processing means supplied with an output of said filtering means indicative of said high spatial frequency components, said processing means evaluating a rate of change of said output of said filtering means with time and producing a control signal indicative of a focusing state of said infrared image on said infrared detection array, based upon said rate of change thus evaluated;

    said processing means supplying said control signal to said lens drive mechanism for controlling the same such that said image plane coincides substantially with said plane of said infrared detection array;

    said processing means comprising a first memory for storing said output signals of said filtering means corresponding to one horizontal scanning line that is included in said two-dimensional image for the present moment, a second memory for storing said output signals of said filtering means corresponding to said horizontal scanning line for a moment in the past, an adder for calculating a sum of a content of said first memory and a content of said second memory, a subtracter for calculating a difference between said content of said first memory and said content of said second memory, and a logic circuit supplied with an output of said adder and an output of said subtracter for producing said control signal indicative of said focusing state based upon a combination of said output of said adder and said output of said subtracter.

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