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Low-light-level imaging and image processing

  • US 5,880,777 A
  • Filed: 04/15/1996
  • Issued: 03/09/1999
  • Est. Priority Date: 04/15/1996
  • Status: Expired due to Fees
First Claim
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1. An imaging system for imaging a scene to produce a sequence of image frames of the scene at a frame rate, R, of at least about 25 image frames per second, the imaging system comprising:

  • an optical input port for accepting input light from the scene;

    a charge-coupled imaging device comprising an array of pixels configured in a charge storage medium, the charge-coupled imaging device located in relation to the input port such that input light from the scene impinges device pixels, the charge-coupled imaging device producing an electrical pixel signal of analog pixel values based on the input light;

    an analog signal processor connected to the charge-coupled imaging device for amplifying the pixel signal;

    an analog-to-digital processor connected to the analog signal processor for digitizing the amplified pixel signal to produce a digital image signal formatted as a sequence of image frames each of a plurality of digital pixel values and having a dynamic range of digital pixel values represented by a number of digital bits, B, where B is greater than 8; and

    a digital image processor connected to the analog-to-digital processor for processing digital pixel values in the sequence of image frames to produce an output image frame sequence at the frame rate, R, representative of the imaged scene, with a latency of no more than about 1/R;

    the output image frame sequence being characterized by noise-limited resolution of at least a minimum number, NM, of line pairs per millimeter, referred to the charge-coupled imaging device pixel array, in an imaged scene as a function of illuminance of the input light impinging the charge-coupled imaging device pixels, wherein for a scene characterized by a contrast of about 0.3, for a human observation time of about 0.05 seconds, and for an image scene frame rate of about 30 frames per second, NM is given as NM =1900 L0.51, where L is the value of illuminance of the input light impinging the charge-coupled imaging device pixels, for at least one illuminance value between a range of illuminance values of about 1×

    10-2 LUX and 5×

    10-7 LUX.

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